Use strict equality when comparing with null, especially when null is a default value.

runtime/bin/file_impl.dart

 // Copyright (c) 2011, 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 _FileInputStream implements FileInputStream {
   _FileInputStream(File file) {
     _file = new File(file.name);
     _file.openSync();
   }
 
@@ skipping 14 matching lines @@
     if (bytesRead < bytesToRead) {
       List<int> newBuffer = new List<int>(bytesRead);
       newBuffer.copyFrom(buffer, 0, 0, bytesRead);
       return newBuffer;
     } else {
       return buffer;
     }
   }
 
   int readInto(List<int> buffer, int offset, int len) {
-    if (offset == null) offset = 0;
-    if (len == null) len = buffer.length;
+    if (offset === null) offset = 0;
+    if (len === null) len = buffer.length;
     if (offset < 0) throw new StreamException("Illegal offset $offset");
     if (len < 0) throw new StreamException("Illegal length $len");
     return _file.readListSync(buffer, offset, len);
   }
 
   int available() {
     return _file.lengthSync() - _file.positionSync();
   }
 
   bool closed() {
@@ skipping 274 matching lines @@
 
   var _existsHandler;
   var _createHandler;
   var _openHandler;
   var _closeHandler;
   var _readByteHandler;
   var _readListHandler;
   var _noPendingWriteHandler;
   var _errorHandler;
 }