a === b -> identical(a, b)

sdk/lib/crypto/crypto_utils.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class _LineWrappingStringBuffer {
   _LineWrappingStringBuffer(int this._lineLength) : _sb = new StringBuffer();
 
   void add(String s) {
-    if (_lineLength !== null && _currentLineLength == _lineLength) {
+    if (_lineLength != null && _currentLineLength == _lineLength) {
       _sb.add('\r\n');
       _currentLineLength = 0;
     }
     _sb.add(s);
     _currentLineLength++;
   }
 
   String toString() => _sb.toString();
 
   int _lineLength;
@@ skipping 45 matching lines @@
       var b1 = bytes[i + 1] & 0xff;
       result.add(table[b0 >> 2]);
       result.add(table[((b0 << 4) | (b1 >> 4)) & 0x3f]);
       result.add(table[(b1 << 2) & 0x3f]);
       result.add('=');
     }
 
     return result.toString();
   }
 }