diff --git a/.travis.yml b/.travis.yml
index a49fc6f..785c7c2 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,21 +1,34 @@
 language: dart
 
 dart:
-  - dev
-dart_task:
-  - test: -p vm,chrome
-  - dartanalyzer
+ - be/raw/latest
 
-matrix:
+jobs:
   include:
-    # Only validate formatting using the dev release
-    - dart: dev
-      dart_task: dartfmt
+    - stage: analyze_and_format
+      name: "Analyze"
+      dart: be/raw/latest
+      os: linux
+      script: dartanalyzer --enable-experiment=non-nullable --fatal-warnings --fatal-infos .
+    - stage: analyze_and_format
+      name: "Format"
+      dart: be/raw/latest
+      os: linux
+      script: dartfmt -n --set-exit-if-changed .
+    - stage: test
+      name: "Vm Tests"
+      dart: be/raw/latest
+      os: linux
+      script: pub run --enable-experiment=non-nullable test -p vm 
+
+stages:
+  - analyze_and_format
+  - test
 
 # Only building master means that we don't run two builds for each pull request.
 branches:
-  only: [master]
+  only: [master, null_safety]
 
 cache:
- directories:
-   - $HOME/.pub-cache
+  directories:
+    - $HOME/.pub-cache
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 321c371..bc7c9ef 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.11.0-nullsafety
+
+* Migrate to null safety
+
 ## 0.10.9
 
 * Fix a number of document comment issues.
diff --git a/analysis_options.yaml b/analysis_options.yaml
index 4f9dfb0..86c8367 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -1,5 +1,9 @@
 include: package:pedantic/analysis_options.yaml
 
+analyzer:
+  enable-experiment:
+    - non-nullable
+
 linter:
   rules:
     - comment_references
diff --git a/lib/builder.dart b/lib/builder.dart
index e6b8d82..5c56ca4 100644
--- a/lib/builder.dart
+++ b/lib/builder.dart
@@ -21,9 +21,7 @@
   /// Adds an entry mapping the [targetOffset] to [source].
   void addFromOffset(SourceLocation source, SourceFile targetFile,
       int targetOffset, String identifier) {
-    if (targetFile == null) {
-      throw ArgumentError('targetFile cannot be null');
-    }
+    ArgumentError.checkNotNull(targetFile, 'targetFile');
     _entries.add(Entry(source, targetFile.location(targetOffset), identifier));
   }
 
@@ -33,7 +31,7 @@
   /// `isIdentifier` set to true, this entry is considered to represent an
   /// identifier whose value will be stored in the source map. [isIdentifier]
   /// takes precedence over [target]'s `isIdentifier` value.
-  void addSpan(SourceSpan source, SourceSpan target, {bool isIdentifier}) {
+  void addSpan(SourceSpan source, SourceSpan target, {bool? isIdentifier}) {
     isIdentifier ??= source is SourceMapSpan ? source.isIdentifier : false;
 
     var name = isIdentifier ? source.text : null;
@@ -42,7 +40,7 @@
 
   /// Adds an entry mapping [target] to [source].
   void addLocation(
-      SourceLocation source, SourceLocation target, String identifier) {
+      SourceLocation source, SourceLocation target, String? identifier) {
     _entries.add(Entry(source, target, identifier));
   }
 
@@ -64,7 +62,7 @@
   final SourceLocation target;
 
   /// An identifier name, when this location is the start of an identifier.
-  final String identifierName;
+  final String? identifierName;
 
   /// Creates a new [Entry] mapping [target] to [source].
   Entry(this.source, this.target, this.identifierName);
diff --git a/lib/parser.dart b/lib/parser.dart
index e3044aa..1f8b817 100644
--- a/lib/parser.dart
+++ b/lib/parser.dart
@@ -23,7 +23,8 @@
 // the string represenation.
 // TODO(tjblasi): Ignore the first line of [jsonMap] if the JSON safety string
 // `)]}'` begins the string representation of the map.
-Mapping parse(String jsonMap, {Map<String, Map> otherMaps, mapUrl}) =>
+Mapping parse(String jsonMap,
+        {Map<String, Map>? otherMaps, /*String|Uri*/ Object? mapUrl}) =>
     parseJson(jsonDecode(jsonMap), otherMaps: otherMaps, mapUrl: mapUrl);
 
 /// Parses a source map or source map bundle directly from a json string.
@@ -31,7 +32,8 @@
 /// [mapUrl], which may be either a [String] or a [Uri], indicates the URL of
 /// the source map file itself. If it's passed, any URLs in the source
 /// map will be interpreted as relative to this URL when generating spans.
-Mapping parseExtended(String jsonMap, {Map<String, Map> otherMaps, mapUrl}) =>
+Mapping parseExtended(String jsonMap,
+        {Map<String, Map>? otherMaps, /*String|Uri*/ Object? mapUrl}) =>
     parseJsonExtended(jsonDecode(jsonMap),
         otherMaps: otherMaps, mapUrl: mapUrl);
 
@@ -40,8 +42,8 @@
 /// [mapUrl], which may be either a [String] or a [Uri], indicates the URL of
 /// the source map file itself. If it's passed, any URLs in the source
 /// map will be interpreted as relative to this URL when generating spans.
-Mapping parseJsonExtended(/*List|Map*/ json,
-    {Map<String, Map> otherMaps, mapUrl}) {
+Mapping parseJsonExtended(/*List|Map*/ Object? json,
+    {Map<String, Map>? otherMaps, /*String|Uri*/ Object? mapUrl}) {
   if (json is List) {
     return MappingBundle.fromJson(json, mapUrl: mapUrl);
   }
@@ -53,7 +55,8 @@
 /// [mapUrl], which may be either a [String] or a [Uri], indicates the URL of
 /// the source map file itself. If it's passed, any URLs in the source
 /// map will be interpreted as relative to this URL when generating spans.
-Mapping parseJson(Map map, {Map<String, Map> otherMaps, mapUrl}) {
+Mapping parseJson(Map map,
+    {Map<String, Map>? otherMaps, /*String|Uri*/ Object? mapUrl}) {
   if (map['version'] != 3) {
     throw ArgumentError('unexpected source map version: ${map["version"]}. '
         'Only version 3 is supported.');
@@ -79,12 +82,12 @@
   /// [uri] is the optional location of the output file to find the span for
   /// to disambiguate cases where a mapping may have different mappings for
   /// different output files.
-  SourceMapSpan spanFor(int line, int column,
-      {Map<String, SourceFile> files, String uri});
+  SourceMapSpan? spanFor(int line, int column,
+      {Map<String, SourceFile>? files, String? uri});
 
   /// Returns the span associated with [location].
-  SourceMapSpan spanForLocation(SourceLocation location,
-      {Map<String, SourceFile> files}) {
+  SourceMapSpan? spanForLocation(SourceLocation location,
+      {Map<String, SourceFile>? files}) {
     return spanFor(location.line, location.column,
         uri: location.sourceUrl?.toString(), files: files);
   }
@@ -103,8 +106,8 @@
   final List<Mapping> _maps = <Mapping>[];
 
   /// Creates a section mapping from json.
-  MultiSectionMapping.fromJson(List sections, Map<String, Map> otherMaps,
-      {mapUrl}) {
+  MultiSectionMapping.fromJson(List sections, Map<String, Map>? otherMaps,
+      {/*String|Uri*/ Object? mapUrl}) {
     for (var section in sections) {
       var offset = section['offset'];
       if (offset == null) throw FormatException('section missing offset');
@@ -124,12 +127,13 @@
       if (url != null && map != null) {
         throw FormatException("section can't use both url and map entries");
       } else if (url != null) {
-        if (otherMaps == null || otherMaps[url] == null) {
+        var other = otherMaps?[url];
+        if (otherMaps == null || other == null) {
           throw FormatException(
               'section contains refers to $url, but no map was '
               'given for it. Make sure a map is passed in "otherMaps"');
         }
-        _maps.add(parseJson(otherMaps[url], otherMaps: otherMaps, mapUrl: url));
+        _maps.add(parseJson(other, otherMaps: otherMaps, mapUrl: url));
       } else if (map != null) {
         _maps.add(parseJson(map, otherMaps: otherMaps, mapUrl: mapUrl));
       } else {
@@ -141,7 +145,7 @@
     }
   }
 
-  int _indexFor(line, column) {
+  int _indexFor(int line, int column) {
     for (var i = 0; i < _lineStart.length; i++) {
       if (line < _lineStart[i]) return i - 1;
       if (line == _lineStart[i] && column < _columnStart[i]) return i - 1;
@@ -150,8 +154,8 @@
   }
 
   @override
-  SourceMapSpan spanFor(int line, int column,
-      {Map<String, SourceFile> files, String uri}) {
+  SourceMapSpan? spanFor(int line, int column,
+      {Map<String, SourceFile>? files, String? uri}) {
     // TODO(jacobr): perhaps verify that targetUrl matches the actual uri
     // or at least ends in the same file name.
     var index = _indexFor(line, column);
@@ -183,7 +187,7 @@
 
   MappingBundle();
 
-  MappingBundle.fromJson(List json, {String mapUrl}) {
+  MappingBundle.fromJson(List json, {/*String|Uri*/ Object? mapUrl}) {
     for (var map in json) {
       addMapping(parseJson(map, mapUrl: mapUrl) as SingleMapping);
     }
@@ -192,7 +196,10 @@
   void addMapping(SingleMapping mapping) {
     // TODO(jacobr): verify that targetUrl is valid uri instead of a windows
     // path.
-    _mappings[mapping.targetUrl] = mapping;
+    // TODO: Remove type arg https://github.com/dart-lang/sdk/issues/42227
+    var targetUrl = ArgumentError.checkNotNull<String>(
+        mapping.targetUrl, 'mapping.targetUrl');
+    _mappings[targetUrl] = mapping;
   }
 
   /// Encodes the Mapping mappings as a json map.
@@ -210,11 +217,10 @@
   bool containsMapping(String url) => _mappings.containsKey(url);
 
   @override
-  SourceMapSpan spanFor(int line, int column,
-      {Map<String, SourceFile> files, String uri}) {
-    if (uri == null) {
-      throw ArgumentError.notNull('uri');
-    }
+  SourceMapSpan? spanFor(int line, int column,
+      {Map<String, SourceFile>? files, String? uri}) {
+    // TODO: Remove type arg https://github.com/dart-lang/sdk/issues/42227
+    uri = ArgumentError.checkNotNull<String>(uri, 'uri');
 
     // Find the longest suffix of the uri that matches the sourcemap
     // where the suffix starts after a path segment boundary.
@@ -232,9 +238,10 @@
     for (var i = 0; i < uri.length; ++i) {
       if (onBoundary) {
         var candidate = uri.substring(i);
-        if (_mappings.containsKey(candidate)) {
-          return _mappings[candidate]
-              .spanFor(line, column, files: files, uri: candidate);
+        var candidateMapping = _mappings[candidate];
+        if (candidateMapping != null) {
+          return candidateMapping.spanFor(line, column,
+              files: files, uri: candidate);
         }
       }
       onBoundary = separatorCodeUnits.contains(uri.codeUnitAt(i));
@@ -270,18 +277,18 @@
   /// field.
   ///
   /// Files whose contents aren't available are `null`.
-  final List<SourceFile> files;
+  final List<SourceFile?> files;
 
   /// Entries indicating the beginning of each span.
   final List<TargetLineEntry> lines;
 
   /// Url of the target file.
-  String targetUrl;
+  String? targetUrl;
 
   /// Source root prepended to all entries in [urls].
-  String sourceRoot;
+  String? sourceRoot;
 
-  final Uri _mapUrl;
+  final Uri? _mapUrl;
 
   final Map<String, dynamic> extensions;
 
@@ -290,9 +297,9 @@
         extensions = {};
 
   factory SingleMapping.fromEntries(Iterable<builder.Entry> entries,
-      [String fileUrl]) {
+      [String? fileUrl]) {
     // The entries needs to be sorted by the target offsets.
-    var sourceEntries = List.from(entries)..sort();
+    var sourceEntries = entries.toList()..sort();
     var lines = <TargetLineEntry>[];
 
     // Indices associated with file urls that will be part of the source map. We
@@ -307,7 +314,7 @@
     var files = <int, SourceFile>{};
 
     var lineNum;
-    List<TargetEntry> targetEntries;
+    late List<TargetEntry> targetEntries;
     for (var sourceEntry in sourceEntries) {
       if (lineNum == null || sourceEntry.target.line > lineNum) {
         lineNum = sourceEntry.target.line;
@@ -315,24 +322,21 @@
         lines.add(TargetLineEntry(lineNum, targetEntries));
       }
 
-      if (sourceEntry.source == null) {
-        targetEntries.add(TargetEntry(sourceEntry.target.column));
-      } else {
-        var sourceUrl = sourceEntry.source.sourceUrl;
-        var urlId = urls.putIfAbsent(
-            sourceUrl == null ? '' : sourceUrl.toString(), () => urls.length);
+      var sourceUrl = sourceEntry.source.sourceUrl;
+      var urlId = urls.putIfAbsent(
+          sourceUrl == null ? '' : sourceUrl.toString(), () => urls.length);
 
-        if (sourceEntry.source is FileLocation) {
-          files.putIfAbsent(
-              urlId, () => (sourceEntry.source as FileLocation).file);
-        }
-
-        var srcNameId = sourceEntry.identifierName == null
-            ? null
-            : names.putIfAbsent(sourceEntry.identifierName, () => names.length);
-        targetEntries.add(TargetEntry(sourceEntry.target.column, urlId,
-            sourceEntry.source.line, sourceEntry.source.column, srcNameId));
+      if (sourceEntry.source is FileLocation) {
+        files.putIfAbsent(
+            urlId, () => (sourceEntry.source as FileLocation).file);
       }
+
+      var sourceEntryIdentifierName = sourceEntry.identifierName;
+      var srcNameId = sourceEntryIdentifierName == null
+          ? null
+          : names.putIfAbsent(sourceEntryIdentifierName, () => names.length);
+      targetEntries.add(TargetEntry(sourceEntry.target.column, urlId,
+          sourceEntry.source.line, sourceEntry.source.column, srcNameId));
     }
     return SingleMapping._(fileUrl, urls.values.map((i) => files[i]).toList(),
         urls.keys.toList(), names.keys.toList(), lines);
@@ -342,14 +346,14 @@
       : targetUrl = map['file'],
         urls = List<String>.from(map['sources']),
         names = List<String>.from(map['names'] ?? []),
-        files = List(map['sources'].length),
+        files = List.filled(map['sources'].length, null),
         sourceRoot = map['sourceRoot'],
         lines = <TargetLineEntry>[],
         _mapUrl = mapUrl is String ? Uri.parse(mapUrl) : mapUrl,
         extensions = {} {
     var sourcesContent = map['sourcesContent'] == null
-        ? const []
-        : List<String>.from(map['sourcesContent']);
+        ? const <String?>[]
+        : List<String?>.from(map['sourcesContent']);
     for (var i = 0; i < urls.length && i < sourcesContent.length; i++) {
       var source = sourcesContent[i];
       if (source == null) continue;
@@ -459,11 +463,11 @@
         var newUrlId = segment.sourceUrlId;
         if (newUrlId == null) continue;
         srcUrlId = _append(buff, srcUrlId, newUrlId);
-        srcLine = _append(buff, srcLine, segment.sourceLine);
-        srcColumn = _append(buff, srcColumn, segment.sourceColumn);
+        srcLine = _append(buff, srcLine, segment.sourceLine!);
+        srcColumn = _append(buff, srcColumn, segment.sourceColumn!);
 
         if (segment.sourceNameId == null) continue;
-        srcNameId = _append(buff, srcNameId, segment.sourceNameId);
+        srcNameId = _append(buff, srcNameId, segment.sourceNameId!);
       }
     }
 
@@ -474,7 +478,7 @@
       'names': names,
       'mappings': buff.toString()
     };
-    if (targetUrl != null) result['file'] = targetUrl;
+    if (targetUrl != null) result['file'] = targetUrl!;
 
     if (includeSourceContents) {
       result['sourcesContent'] = files.map((file) => file?.getText(0)).toList();
@@ -498,7 +502,7 @@
   /// Returns [TargetLineEntry] which includes the location in the target [line]
   /// number. In particular, the resulting entry is the last entry whose line
   /// number is lower or equal to [line].
-  TargetLineEntry _findLine(int line) {
+  TargetLineEntry? _findLine(int line) {
     var index = binarySearch(lines, (e) => e.line > line);
     return (index <= 0) ? null : lines[index - 1];
   }
@@ -508,7 +512,7 @@
   /// the last entry whose column is lower or equal than [column]. If
   /// [lineEntry] corresponds to a line prior to [line], then the result will be
   /// the very last entry on that line.
-  TargetEntry _findColumn(int line, int column, TargetLineEntry lineEntry) {
+  TargetEntry? _findColumn(int line, int column, TargetLineEntry? lineEntry) {
     if (lineEntry == null || lineEntry.entries.isEmpty) return null;
     if (lineEntry.line != line) return lineEntry.entries.last;
     var entries = lineEntry.entries;
@@ -517,33 +521,39 @@
   }
 
   @override
-  SourceMapSpan spanFor(int line, int column,
-      {Map<String, SourceFile> files, String uri}) {
+  SourceMapSpan? spanFor(int line, int column,
+      {Map<String, SourceFile>? files, String? uri}) {
     var entry = _findColumn(line, column, _findLine(line));
-    if (entry == null || entry.sourceUrlId == null) return null;
-    var url = urls[entry.sourceUrlId];
+    if (entry == null) return null;
+
+    var sourceUrlId = entry.sourceUrlId;
+    if (sourceUrlId == null) return null;
+
+    var url = urls[sourceUrlId];
     if (sourceRoot != null) {
       url = '${sourceRoot}${url}';
     }
-    if (files != null && files[url] != null) {
-      var file = files[url];
-      var start = file.getOffset(entry.sourceLine, entry.sourceColumn);
-      if (entry.sourceNameId != null) {
-        var text = names[entry.sourceNameId];
-        return SourceMapFileSpan(files[url].span(start, start + text.length),
+
+    var sourceNameId = entry.sourceNameId;
+    var file = files?[url];
+    if (file != null) {
+      var start = file.getOffset(entry.sourceLine!, entry.sourceColumn);
+      if (sourceNameId != null) {
+        var text = names[sourceNameId];
+        return SourceMapFileSpan(file.span(start, start + text.length),
             isIdentifier: true);
       } else {
-        return SourceMapFileSpan(files[url].location(start).pointSpan());
+        return SourceMapFileSpan(file.location(start).pointSpan());
       }
     } else {
       var start = SourceLocation(0,
-          sourceUrl: _mapUrl == null ? url : _mapUrl.resolve(url),
+          sourceUrl: _mapUrl?.resolve(url) ?? url,
           line: entry.sourceLine,
           column: entry.sourceColumn);
 
       // Offset and other context is not available.
-      if (entry.sourceNameId != null) {
-        return SourceMapSpan.identifier(start, names[entry.sourceNameId]);
+      if (sourceNameId != null) {
+        return SourceMapSpan.identifier(start, names[sourceNameId]);
       } else {
         return SourceMapSpan(start, start, '');
       }
@@ -578,18 +588,20 @@
           ..write(line)
           ..write(':')
           ..write(entry.column);
-        if (entry.sourceUrlId != null) {
+        var sourceUrlId = entry.sourceUrlId;
+        if (sourceUrlId != null) {
           buff
             ..write('   -->   ')
             ..write(sourceRoot)
-            ..write(urls[entry.sourceUrlId])
+            ..write(urls[sourceUrlId])
             ..write(': ')
             ..write(entry.sourceLine)
             ..write(':')
             ..write(entry.sourceColumn);
         }
-        if (entry.sourceNameId != null) {
-          buff..write(' (')..write(names[entry.sourceNameId])..write(')');
+        var sourceNameId = entry.sourceNameId;
+        if (sourceNameId != null) {
+          buff..write(' (')..write(names[sourceNameId])..write(')');
         }
         buff.write('\n');
       }
@@ -611,10 +623,10 @@
 /// A target segment entry read from a source map
 class TargetEntry {
   final int column;
-  final int sourceUrlId;
-  final int sourceLine;
-  final int sourceColumn;
-  final int sourceNameId;
+  final int? sourceUrlId;
+  final int? sourceLine;
+  final int? sourceColumn;
+  final int? sourceNameId;
 
   TargetEntry(this.column,
       [this.sourceUrlId,
@@ -639,9 +651,11 @@
   // Iterator API is used by decodeVlq to consume VLQ entries.
   @override
   bool moveNext() => ++index < _length;
+
   @override
-  String get current =>
-      (index >= 0 && index < _length) ? _internal[index] : null;
+  String get current => (index >= 0 && index < _length)
+      ? _internal[index]
+      : throw RangeError.index(index, _internal);
 
   bool get hasTokens => index < _length - 1 && _length > 0;
 
@@ -671,7 +685,9 @@
       buff.write(_internal[i]);
     }
     buff.write('[31m');
-    buff.write(current ?? '');
+    try {
+      buff.write(current);
+    } on RangeError catch (_) {}
     buff.write('[0m');
     for (var i = index + 1; i < _internal.length; i++) {
       buff.write(_internal[i]);
diff --git a/lib/printer.dart b/lib/printer.dart
index d79d2cb..922c7fe 100644
--- a/lib/printer.dart
+++ b/lib/printer.dart
@@ -23,7 +23,7 @@
   String get map => _maps.toJson(filename);
 
   /// Current source location mapping.
-  SourceLocation _loc;
+  SourceLocation? _loc;
 
   /// Current line in the buffer;
   int _line = 0;
@@ -47,13 +47,21 @@
         // Return not followed by line-feed is treated as a new line.
         _line++;
         _column = 0;
-        if (projectMarks && _loc != null) {
-          if (_loc is FileLocation) {
-            var file = (_loc as FileLocation).file;
-            mark(file.location(file.getOffset(_loc.line + 1)));
-          } else {
-            mark(SourceLocation(0,
-                sourceUrl: _loc.sourceUrl, line: _loc.line + 1, column: 0));
+        {
+          // **Warning**: Any calls to `mark` will change the value of `_loc`,
+          // so this local variable is no longer up to date after that point.
+          //
+          // This is why it has been put inside its own block to limit the
+          // scope in which it is available.
+          var loc = _loc;
+          if (projectMarks && loc != null) {
+            if (loc is FileLocation) {
+              var file = loc.file;
+              mark(file.location(file.getOffset(loc.line + 1)));
+            } else {
+              mark(SourceLocation(0,
+                  sourceUrl: loc.sourceUrl, line: loc.line + 1, column: 0));
+            }
           }
         }
       } else {
@@ -78,8 +86,8 @@
   /// this also records the name of the identifier in the source map
   /// information.
   void mark(mark) {
-    SourceLocation loc;
-    String identifier;
+    late final SourceLocation loc;
+    String? identifier;
     if (mark is SourceLocation) {
       loc = mark;
     } else if (mark is SourceSpan) {
@@ -106,11 +114,20 @@
   final _items = <dynamic>[];
 
   /// Internal buffer to merge consecutive strings added to this printer.
-  StringBuffer _buff;
+  StringBuffer? _buff;
 
   /// Current indentation, which can be updated from outside this class.
   int indent;
 
+  /// [Printer] used during the last call to [build], if any.
+  Printer? printer;
+
+  /// Returns the text produced after calling [build].
+  String? get text => printer?.text;
+
+  /// Returns the source-map information produced after calling [build].
+  String? get map => printer?.map;
+
   /// Item used to indicate that the following item is copied from the original
   /// source code, and hence we should preserve source-maps on every new line.
   static final _ORIGINAL = Object();
@@ -133,7 +150,7 @@
   /// Setting [isOriginal] will make this printer propagate source map locations
   /// on every line-break.
   void add(object,
-      {SourceLocation location, SourceSpan span, bool isOriginal = false}) {
+      {SourceLocation? location, SourceSpan? span, bool isOriginal = false}) {
     if (object is! String || location != null || span != null || isOriginal) {
       _flush();
       assert(location == null || span == null);
@@ -162,7 +179,7 @@
   /// The [location] and [span] parameters indicate the corresponding source map
   /// location of [line] in the original input. Only one, [location] or
   /// [span], should be provided at a time.
-  void addLine(String line, {SourceLocation location, SourceSpan span}) {
+  void addLine(String? line, {SourceLocation? location, SourceSpan? span}) {
     if (location != null || span != null) {
       _flush();
       assert(location == null || span == null);
@@ -180,8 +197,8 @@
 
   /// Appends a string merging it with any previous strings, if possible.
   void _appendString(String s) {
-    _buff ??= StringBuffer();
-    _buff.write(s);
+    var buf = _buff ??= StringBuffer();
+    buf.write(s);
   }
 
   /// Adds all of the current [_buff] contents as a string item.
@@ -206,15 +223,6 @@
     return (StringBuffer()..writeAll(_items)).toString();
   }
 
-  /// [Printer] used during the last call to [build], if any.
-  Printer printer;
-
-  /// Returns the text produced after calling [build].
-  String get text => printer.text;
-
-  /// Returns the source-map information produced after calling [build].
-  String get map => printer.map;
-
   /// Builds the output of this printer and source map information. After
   /// calling this function, you can use [text] and [map] to retrieve the
   /// geenrated code and source map information, respectively.
diff --git a/lib/refactor.dart b/lib/refactor.dart
index 5e117e8..64fd610 100644
--- a/lib/refactor.dart
+++ b/lib/refactor.dart
@@ -17,7 +17,7 @@
 /// Applies a series of edits using original location
 /// information, and composes them into the edited string.
 class TextEditTransaction {
-  final SourceFile file;
+  final SourceFile? file;
   final String original;
   final _edits = <_TextEdit>[];
 
@@ -33,9 +33,9 @@
     _edits.add(_TextEdit(begin, end, replacement));
   }
 
-  /// Create a source map [SourceLocation] for [offset].
-  SourceLocation _loc(int offset) =>
-      file != null ? file.location(offset) : null;
+  /// Create a source map [SourceLocation] for [offset], if [file] is not
+  /// `null`.
+  SourceLocation? _loc(int offset) => file?.location(offset);
 
   /// Applies all pending [edit]s and returns a [NestedPrinter] containing the
   /// rewritten string and source map information. [file]`.location` is given to
@@ -58,7 +58,7 @@
       if (consumed > edit.begin) {
         var sb = StringBuffer();
         sb
-          ..write(file.location(edit.begin).toolString)
+          ..write(file?.location(edit.begin).toolString)
           ..write(': overlapping edits. Insert at offset ')
           ..write(edit.begin)
           ..write(' but have consumed ')
diff --git a/lib/src/source_map_span.dart b/lib/src/source_map_span.dart
index b8f1152..65574ca 100644
--- a/lib/src/source_map_span.dart
+++ b/lib/src/source_map_span.dart
@@ -52,7 +52,7 @@
   @override
   String get context => _inner.context;
   @override
-  Uri get sourceUrl => _inner.sourceUrl;
+  Uri? get sourceUrl => _inner.sourceUrl;
   @override
   int get length => _inner.length;
 
diff --git a/lib/src/vlq.dart b/lib/src/vlq.dart
index d4e29a1..951ea8b 100644
--- a/lib/src/vlq.dart
+++ b/lib/src/vlq.dart
@@ -33,8 +33,8 @@
   return map;
 }();
 
-final int MAX_INT32 = pow(2, 31) - 1;
-final int MIN_INT32 = -pow(2, 31);
+final int MAX_INT32 = (pow(2, 31) as int) - 1;
+final int MIN_INT32 = -(pow(2, 31) as int);
 
 /// Creates the VLQ encoding of [value] as a sequence of characters
 Iterable<String> encodeVlq(int value) {
@@ -70,10 +70,10 @@
   while (!stop) {
     if (!chars.moveNext()) throw StateError('incomplete VLQ value');
     var char = chars.current;
-    if (!_digits.containsKey(char)) {
+    var digit = _digits[char];
+    if (digit == null) {
       throw FormatException('invalid character in VLQ encoding: $char');
     }
-    var digit = _digits[char];
     stop = (digit & VLQ_CONTINUATION_BIT) == 0;
     digit &= VLQ_BASE_MASK;
     result += (digit << shift);
diff --git a/pubspec.yaml b/pubspec.yaml
index 871c40a..a59c77d 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,16 +1,93 @@
 name: source_maps
-version: 0.10.9
+version: 0.11.0-nullsafety
 
 description: Library to programmatically manipulate source map files.
 homepage: https://github.com/dart-lang/source_maps
 
 environment:
-  sdk: '>=2.0.0 <3.0.0'
+  sdk: '>=2.9.0-18.0 <2.9.0'
 
 dependencies:
-  source_span: ^1.3.0
+  source_span: '>=1.8.0-nullsafety <1.8.0'
 
 dev_dependencies:
-  source_span: ^1.5.4
   test: ^1.2.0
   term_glyph: ^1.0.0
+
+dependency_overrides:
+  # Overrides required for a version solve
+  coverage: 0.14.0
+  # NNBD Branches
+  async:
+    git:
+      url: git://github.com/dart-lang/async.git
+      ref: null_safety
+  boolean_selector:
+    git:
+      url: git://github.com/dart-lang/boolean_selector.git
+      ref: null_safety
+  charcode:
+    git:
+      url: git://github.com/dart-lang/charcode.git
+      ref: null_safety
+  collection: 1.15.0-nullsafety
+  js:
+    git:
+      url: git://github.com/dart-lang/sdk.git
+      path: pkg/js
+  matcher:
+    git:
+      url: git://github.com/dart-lang/matcher.git
+      ref: null_safety
+  meta: 1.3.0-nullsafety
+  path:
+    git:
+      url: git://github.com/dart-lang/path.git
+      ref: null_safety
+  pedantic:
+    git:
+      url: git://github.com/dart-lang/pedantic.git
+      ref: null_safety
+  pool:
+    git:
+      url: git://github.com/dart-lang/pool.git
+      ref: null_safety
+  source_map_stack_trace:
+    git:
+      url: git://github.com/dart-lang/source_map_stack_trace.git
+      ref: null_safety
+  source_span:
+    git:
+      url: git://github.com/dart-lang/source_span.git
+      ref: null_safety
+  stack_trace:
+    git:
+      url: git://github.com/dart-lang/stack_trace.git
+      ref: null_safety
+  stream_channel:
+    git:
+      url: git://github.com/dart-lang/stream_channel.git
+      ref: null_safety
+  string_scanner:
+    git:
+      url: git://github.com/dart-lang/string_scanner.git
+      ref: null_safety
+  term_glyph:
+    git:
+      url: git://github.com/dart-lang/term_glyph.git
+      ref: null_safety
+  test:
+    git:
+      url: git://github.com/dart-lang/test.git
+      ref: null_safety
+      path: pkgs/test
+  test_api:
+    git:
+      url: git://github.com/dart-lang/test.git
+      ref: null_safety
+      path: pkgs/test_api
+  test_core:
+    git:
+      url: git://github.com/dart-lang/test.git
+      ref: null_safety
+      path: pkgs/test_core
diff --git a/test/common.dart b/test/common.dart
index c0bed68..6ba1c67 100644
--- a/test/common.dart
+++ b/test/common.dart
@@ -76,8 +76,8 @@
   var line = outputSpan.start.line;
   var column = outputSpan.start.column;
   var files = realOffsets ? {'input.dart': input} : null;
-  var span = mapping.spanFor(line, column, files: files);
-  var span2 = mapping.spanForLocation(outputSpan.start, files: files);
+  var span = mapping.spanFor(line, column, files: files)!;
+  var span2 = mapping.spanForLocation(outputSpan.start, files: files)!;
 
   // Both mapping APIs are equivalent.
   expect(span.start.offset, span2.start.offset);
diff --git a/test/parser_test.dart b/test/parser_test.dart
index 1b73f13..1b3ae6f 100644
--- a/test/parser_test.dart
+++ b/test/parser_test.dart
@@ -104,7 +104,7 @@
   });
 
   test('parse with no source location', () {
-    SingleMapping map = parse(jsonEncode(MAP_WITH_NO_SOURCE_LOCATION));
+    var map = parse(jsonEncode(MAP_WITH_NO_SOURCE_LOCATION)) as SingleMapping;
     expect(map.lines.length, 1);
     expect(map.lines.first.entries.length, 1);
     var entry = map.lines.first.entries.first;
@@ -117,7 +117,7 @@
   });
 
   test('parse with source location and no name', () {
-    SingleMapping map = parse(jsonEncode(MAP_WITH_SOURCE_LOCATION));
+    var map = parse(jsonEncode(MAP_WITH_SOURCE_LOCATION)) as SingleMapping;
     expect(map.lines.length, 1);
     expect(map.lines.first.entries.length, 1);
     var entry = map.lines.first.entries.first;
@@ -130,8 +130,8 @@
   });
 
   test('parse with source location and missing names entry', () {
-    SingleMapping map =
-        parse(jsonEncode(MAP_WITH_SOURCE_LOCATION_AND_MISSING_NAMES));
+    var map = parse(jsonEncode(MAP_WITH_SOURCE_LOCATION_AND_MISSING_NAMES))
+        as SingleMapping;
     expect(map.lines.length, 1);
     expect(map.lines.first.entries.length, 1);
     var entry = map.lines.first.entries.first;
@@ -144,7 +144,8 @@
   });
 
   test('parse with source location and name', () {
-    SingleMapping map = parse(jsonEncode(MAP_WITH_SOURCE_LOCATION_AND_NAME));
+    var map =
+        parse(jsonEncode(MAP_WITH_SOURCE_LOCATION_AND_NAME)) as SingleMapping;
     expect(map.lines.length, 1);
     expect(map.lines.first.entries.length, 1);
     var entry = map.lines.first.entries.first;
@@ -160,12 +161,12 @@
     var inputMap = Map.from(MAP_WITH_SOURCE_LOCATION);
     inputMap['sourceRoot'] = '/pkg/';
     var mapping = parseJson(inputMap) as SingleMapping;
-    expect(mapping.spanFor(0, 0).sourceUrl, Uri.parse('/pkg/input.dart'));
+    expect(mapping.spanFor(0, 0)?.sourceUrl, Uri.parse('/pkg/input.dart'));
     expect(
         mapping
             .spanForLocation(
                 SourceLocation(0, sourceUrl: Uri.parse('ignored.dart')))
-            .sourceUrl,
+            ?.sourceUrl,
         Uri.parse('/pkg/input.dart'));
 
     var newSourceRoot = '/new/';
@@ -180,7 +181,7 @@
     var inputMap = Map.from(MAP_WITH_SOURCE_LOCATION);
     inputMap['sourceRoot'] = 'pkg/';
     var mapping = parseJson(inputMap, mapUrl: 'file:///path/to/map');
-    expect(mapping.spanFor(0, 0).sourceUrl,
+    expect(mapping.spanFor(0, 0)?.sourceUrl,
         Uri.parse('file:///path/to/pkg/input.dart'));
   });
 
@@ -193,29 +194,31 @@
           mapping
               .spanForLocation(SourceLocation(0,
                   sourceUrl: Uri.file('/path/to/output.dart')))
-              .sourceUrl,
+              ?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input1.dart'));
       expect(
           mapping
               .spanForLocation(SourceLocation(0,
                   sourceUrl: Uri.file('/path/to/output2.dart')))
-              .sourceUrl,
+              ?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input2.dart'));
       expect(
           mapping
               .spanForLocation(SourceLocation(0,
                   sourceUrl: Uri.file('/path/to/3/output.dart')))
-              .sourceUrl,
+              ?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input3.dart'));
 
       expect(
-          mapping.spanFor(0, 0, uri: 'file:///path/to/output.dart').sourceUrl,
+          mapping.spanFor(0, 0, uri: 'file:///path/to/output.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input1.dart'));
       expect(
-          mapping.spanFor(0, 0, uri: 'file:///path/to/output2.dart').sourceUrl,
+          mapping.spanFor(0, 0, uri: 'file:///path/to/output2.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input2.dart'));
       expect(
-          mapping.spanFor(0, 0, uri: 'file:///path/to/3/output.dart').sourceUrl,
+          mapping
+              .spanFor(0, 0, uri: 'file:///path/to/3/output.dart')
+              ?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input3.dart'));
     });
 
@@ -224,36 +227,36 @@
           mapping
               .spanForLocation(SourceLocation(0,
                   sourceUrl: Uri.parse('package:1/output.dart')))
-              .sourceUrl,
+              ?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input1.dart'));
       expect(
           mapping
               .spanForLocation(SourceLocation(0,
                   sourceUrl: Uri.parse('package:2/output2.dart')))
-              .sourceUrl,
+              ?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input2.dart'));
       expect(
           mapping
               .spanForLocation(SourceLocation(0,
                   sourceUrl: Uri.parse('package:3/output.dart')))
-              .sourceUrl,
+              ?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input3.dart'));
 
-      expect(mapping.spanFor(0, 0, uri: 'package:1/output.dart').sourceUrl,
+      expect(mapping.spanFor(0, 0, uri: 'package:1/output.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input1.dart'));
-      expect(mapping.spanFor(0, 0, uri: 'package:2/output2.dart').sourceUrl,
+      expect(mapping.spanFor(0, 0, uri: 'package:2/output2.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input2.dart'));
-      expect(mapping.spanFor(0, 0, uri: 'package:3/output.dart').sourceUrl,
+      expect(mapping.spanFor(0, 0, uri: 'package:3/output.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input3.dart'));
     });
 
     test('unmapped path', () {
-      var span = mapping.spanFor(0, 0, uri: 'unmapped_output.dart');
+      var span = mapping.spanFor(0, 0, uri: 'unmapped_output.dart')!;
       expect(span.sourceUrl, Uri.parse('unmapped_output.dart'));
       expect(span.start.line, equals(0));
       expect(span.start.column, equals(0));
 
-      span = mapping.spanFor(10, 5, uri: 'unmapped_output.dart');
+      span = mapping.spanFor(10, 5, uri: 'unmapped_output.dart')!;
       expect(span.sourceUrl, Uri.parse('unmapped_output.dart'));
       expect(span.start.line, equals(10));
       expect(span.start.column, equals(5));
@@ -264,11 +267,11 @@
     });
 
     test('incomplete paths', () {
-      expect(mapping.spanFor(0, 0, uri: 'output.dart').sourceUrl,
+      expect(mapping.spanFor(0, 0, uri: 'output.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input1.dart'));
-      expect(mapping.spanFor(0, 0, uri: 'output2.dart').sourceUrl,
+      expect(mapping.spanFor(0, 0, uri: 'output2.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input2.dart'));
-      expect(mapping.spanFor(0, 0, uri: '3/output.dart').sourceUrl,
+      expect(mapping.spanFor(0, 0, uri: '3/output.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input3.dart'));
     });
 
@@ -276,11 +279,11 @@
       var mapping = parseExtended(jsonEncode(SOURCE_MAP_BUNDLE),
           mapUrl: 'file:///path/to/map');
 
-      expect(mapping.spanFor(0, 0, uri: 'output.dart').sourceUrl,
+      expect(mapping.spanFor(0, 0, uri: 'output.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input1.dart'));
-      expect(mapping.spanFor(0, 0, uri: 'output2.dart').sourceUrl,
+      expect(mapping.spanFor(0, 0, uri: 'output2.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input2.dart'));
-      expect(mapping.spanFor(0, 0, uri: '3/output.dart').sourceUrl,
+      expect(mapping.spanFor(0, 0, uri: '3/output.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input3.dart'));
     });
 
@@ -288,22 +291,22 @@
       var mapping = MappingBundle();
 
       mapping.addMapping(parseJson(MAP_WITH_SOURCE_LOCATION_AND_NAME_1,
-          mapUrl: 'file:///path/to/map'));
-      expect(mapping.spanFor(0, 0, uri: 'output.dart').sourceUrl,
+          mapUrl: 'file:///path/to/map') as SingleMapping);
+      expect(mapping.spanFor(0, 0, uri: 'output.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input1.dart'));
 
       expect(mapping.containsMapping('output2.dart'), isFalse);
       mapping.addMapping(parseJson(MAP_WITH_SOURCE_LOCATION_AND_NAME_2,
-          mapUrl: 'file:///path/to/map'));
+          mapUrl: 'file:///path/to/map') as SingleMapping);
       expect(mapping.containsMapping('output2.dart'), isTrue);
-      expect(mapping.spanFor(0, 0, uri: 'output2.dart').sourceUrl,
+      expect(mapping.spanFor(0, 0, uri: 'output2.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input2.dart'));
 
       expect(mapping.containsMapping('3/output.dart'), isFalse);
       mapping.addMapping(parseJson(MAP_WITH_SOURCE_LOCATION_AND_NAME_3,
-          mapUrl: 'file:///path/to/map'));
+          mapUrl: 'file:///path/to/map') as SingleMapping);
       expect(mapping.containsMapping('3/output.dart'), isTrue);
-      expect(mapping.spanFor(0, 0, uri: '3/output.dart').sourceUrl,
+      expect(mapping.spanFor(0, 0, uri: '3/output.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input3.dart'));
     });
 
@@ -315,31 +318,33 @@
           mapping
               .spanForLocation(SourceLocation(0,
                   sourceUrl: Uri.parse('http://localhost/output.dart')))
-              .sourceUrl,
+              ?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input1.dart'));
       expect(
           mapping
               .spanForLocation(SourceLocation(0,
                   sourceUrl: Uri.parse('http://localhost/output2.dart')))
-              .sourceUrl,
+              ?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input2.dart'));
       expect(
           mapping
               .spanForLocation(SourceLocation(0,
                   sourceUrl: Uri.parse('http://localhost/3/output.dart')))
-              .sourceUrl,
+              ?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input3.dart'));
 
       expect(
-          mapping.spanFor(0, 0, uri: 'http://localhost/output.dart').sourceUrl,
+          mapping.spanFor(0, 0, uri: 'http://localhost/output.dart')?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input1.dart'));
       expect(
-          mapping.spanFor(0, 0, uri: 'http://localhost/output2.dart').sourceUrl,
+          mapping
+              .spanFor(0, 0, uri: 'http://localhost/output2.dart')
+              ?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input2.dart'));
       expect(
           mapping
               .spanFor(0, 0, uri: 'http://localhost/3/output.dart')
-              .sourceUrl,
+              ?.sourceUrl,
           Uri.parse('file:///path/to/pkg/input3.dart'));
     });
   });
@@ -351,10 +356,10 @@
       MAP_WITH_SOURCE_LOCATION,
       MAP_WITH_SOURCE_LOCATION_AND_NAME
     ]) {
-      SingleMapping mapping = parseJson(expected);
+      var mapping = parseJson(expected) as SingleMapping;
       expect(mapping.toJson(), equals(expected));
 
-      mapping = parseJsonExtended(expected);
+      mapping = parseJsonExtended(expected) as SingleMapping;
       expect(mapping.toJson(), equals(expected));
     }
 
@@ -366,7 +371,7 @@
     var map = Map.from(EXPECTED_MAP);
     map['x_foo'] = 'a';
     map['x_bar'] = [3];
-    SingleMapping mapping = parseJson(map);
+    var mapping = parseJson(map) as SingleMapping;
     expect(mapping.toJson(), equals(map));
     expect(mapping.extensions['x_foo'], equals('a'));
     expect(mapping.extensions['x_bar'].first, equals(3));
@@ -415,7 +420,7 @@
         map['sourcesContent'] = ['hello, world!'];
         var mapping = parseJson(map) as SingleMapping;
 
-        var file = mapping.files[0];
+        var file = mapping.files[0]!;
         expect(file.url, equals(Uri.parse('input.dart')));
         expect(file.getText(0), equals('hello, world!'));
       });
diff --git a/test/refactor_test.dart b/test/refactor_test.dart
index 36b934a..9a403a1 100644
--- a/test/refactor_test.dart
+++ b/test/refactor_test.dart
@@ -60,7 +60,7 @@
     txn.edit(34, 35, '___');
     var printer = (txn.commit()..build(''));
     var output = printer.text;
-    var map = parse(printer.map);
+    var map = parse(printer.map!);
     expect(output,
         '0123456789\n0*23456789\n01*34__\n    789\na___cdefghij\nabcd*fghij\n');
 
@@ -197,7 +197,5 @@
   });
 }
 
-String _span(int line, int column, Mapping map, SourceFile file) {
-  var span = map.spanFor(line - 1, column - 1, files: {'': file});
-  return span == null ? null : span.message('').trim();
-}
+String? _span(int line, int column, Mapping map, SourceFile file) =>
+    map.spanFor(line - 1, column - 1, files: {'': file})?.message('').trim();
diff --git a/test/vlq_test.dart b/test/vlq_test.dart
index 6021519..92a8f4a 100644
--- a/test/vlq_test.dart
+++ b/test/vlq_test.dart
@@ -27,8 +27,8 @@
   });
 
   test('only 32-bit ints allowed', () {
-    var max_int = pow(2, 31) - 1;
-    var min_int = -pow(2, 31);
+    var max_int = (pow(2, 31) as int) - 1;
+    var min_int = -(pow(2, 31) as int);
     _checkEncodeDecode(max_int - 1);
     _checkEncodeDecode(min_int + 1);
     _checkEncodeDecode(max_int);