Handle exception and clean-up code

pkg/analyzer/lib/src/generated/source.dart

 // Copyright (c) 2014, 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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.source;
 
 import "dart:math" as math;
@@ skipping 644 matching lines @@
    * Return a source object that is equal to the source object used to obtain the given encoding.
    *
    * @param encoding the encoding of a source object
    * @return a source object that is described by the given encoding
    * @throws IllegalArgumentException if the argument is not a valid encoding
    * See [Source.encoding].
    */
   Source fromEncoding(String encoding) {
     Source source = forUri(encoding);
     if (source == null) {
-      throw new IllegalArgumentException("Invalid source encoding: $encoding");
+      throw new IllegalArgumentException("Invalid source encoding: '$encoding'");
     }
     return source;
   }
 
   /**
    * Determines if the given [Source] is local.
    *
    * @param source the [Source] to analyze
    * @return `true` if the given [Source] is local
    */
@@ skipping 308 matching lines @@
 
   /**
    * Return an absolute URI that represents the given source, or `null` if a valid URI cannot
    * be computed.
    *
    * @param source the source to get URI for
    * @return the absolute URI representing the given source
    */
   Uri restoreAbsolute(Source source) => null;
 }