Small changes to make analyzer happy.

sdk/lib/convert/string_conversion.dart

 // Copyright (c) 2013, 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.
 
 part of dart.convert;
 
 /**
  * This class provides an interface for converters to
  * efficiently transmit String data.
  *
@@ skipping 74 matching lines @@
 class _ClosableStringSink implements ClosableStringSink {
   final _StringSinkCloseCallback _callback;
   final StringSink _sink;
 
   _ClosableStringSink(this._sink, this._callback);
 
   void close() => _callback();
 
   void writeCharCode(int charCode) => _sink.writeCharCode(charCode);
   void write(Object o) => _sink.write(o);
-  void writeln([Object o]) => _sink.writeln(o);
-  void writeAll(Iterable objects, [String separator])
+  void writeln([Object o = ""]) => _sink.writeln(o);
+  void writeAll(Iterable objects, [String separator = ""])
       => _sink.writeAll(objects, separator);
 }
 
 /**
  * This class wraps an existing [StringConversionSink] and exposes a
  * [ClosableStringSink] interface. The wrapped sink only needs to implement
  * `add` and `close`.
  */
 // TODO(floitsch): make this class public?
 class _StringConversionSinkAsStringSinkAdapter implements ClosableStringSink {
@@ skipping 14 matching lines @@
     _buffer.writeCharCode(charCode);
     if (_buffer.length > _MIN_STRING_SIZE) _flush();
   }
 
   void write(Object o) {
     if (_buffer.isNotEmpty) _flush();
     String str = o.toString();
     _chunkedSink.add(o.toString());
   }
 
-  void writeln([Object o]) {
+  void writeln([Object o = ""]) {
     _buffer.writeln(o);
     if (_buffer.length > _MIN_STRING_SIZE) _flush();
   }
 
-  void writeAll(Iterable objects, [String separator]) {
+  void writeAll(Iterable objects, [String separator = ""]) {
     if (_buffer.isNotEmpty) _flush();
     Iterator iterator = objects.iterator;
     if (!iterator.moveNext()) return;
     if (separator.isEmpty) {
       do {
         _chunkedSink.add(iterator.current.toString());
       } while (iterator.moveNext());
     } else {
       _chunkedSink.add(iterator.current.toString());
       while (iterator.moveNext()) {
@@ skipping 183 matching lines @@
     _decoder.convert(chunk, startIndex, endIndex);
     if (_buffer.isNotEmpty) {
       String accumulated = _buffer.toString();
       _chunkedSink.addSlice(accumulated, 0, accumulated.length, isLast);
       _buffer.clear();
       return;
     }
     if (isLast) close();
   }
 }