prefer isDartCoreObject (#2108)

diff --git a/lib/src/rules/overridden_fields.dart b/lib/src/rules/overridden_fields.dart
index 2e78456..717f282 100644
--- a/lib/src/rules/overridden_fields.dart
+++ b/lib/src/rules/overridden_fields.dart
@@ -69,7 +69,7 @@
 Iterable<InterfaceType> _findAllSupertypesAndMixins(
     InterfaceType interface, List<InterfaceType> accumulator) {
   if (interface == null ||
-      interface.isObject ||
+      interface.isDartCoreObject ||
       accumulator.contains(interface)) {
     return accumulator;
   }
diff --git a/lib/src/util/dart_type_utilities.dart b/lib/src/util/dart_type_utilities.dart
index ffe2087..8ca7689 100644
--- a/lib/src/util/dart_type_utilities.dart
+++ b/lib/src/util/dart_type_utilities.dart
@@ -458,7 +458,7 @@
         // Otherwise, they might be related.
         return false;
       } else {
-        return leftElement.supertype?.isObject == true ||
+        return leftElement.supertype?.isDartCoreObject == true ||
             leftElement.supertype != rightElement.supertype;
       }
     } else if (leftType is TypeParameterType &&
diff --git a/lib/src/util/unrelated_types_visitor.dart b/lib/src/util/unrelated_types_visitor.dart
index 69644c0..74133cc 100644
--- a/lib/src/util/unrelated_types_visitor.dart
+++ b/lib/src/util/unrelated_types_visitor.dart
@@ -44,7 +44,7 @@
     InterfaceTypeDefinition definition, InterfaceType type,
     {List<InterfaceType> accumulator = const []}) {
   if (type == null ||
-      type.isObject ||
+      type.isDartCoreObject ||
       type.isDynamic ||
       accumulator.contains(type)) {
     return null;