library test /*isNonNullableByDefault*/;
import self as self;
import "dart:core" as core;

static method foo(dynamic obj) → core::String?
  return obj is{ForNonNullableByDefault} core::String ?{core::String?} obj{core::String}.{core::String::toUpperCase}(){() → core::String} : null;
static method main() → dynamic {}