Handle exception while getting modification stamp

pkg/analyzer/lib/src/generated/engine.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;
 
 import "dart:math" as math;
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    * not known. The line information is used to map offsets from the beginning of the source to line
    * and column pairs.
    *
    * @param source the source whose line information is to be returned
    * @return the line information for the given source
    * See [computeLineInfo].
    */
   LineInfo getLineInfo(Source source);
 
   /**
-   * Return the modification stamp for the given source. A modification stamp is a non-negative
-   * integer with the property that if the contents of the source have not been modified since the
-   * last time the modification stamp was accessed then the same value will be returned, but if the
-   * contents of the source have been modified one or more times (even if the net change is zero)
-   * the stamps will be different.
+   * Return the modification stamp for the [source], or a negative value if the
+   * source does not exist. A modification stamp is a non-negative integer with
+   * the property that if the contents of the source have not been modified
+   * since the last time the modification stamp was accessed then the same value
+   * will be returned, but if the contents of the source have been modified one
+   * or more times (even if the net change is zero) the stamps will be different.
    *
-   * This method should be used rather than the method [Source.getModificationStamp] because
-   * contexts can have local overrides of the content of a source that the source is not aware of.
-   *
-   * @param source the source whose modification stamp is to be returned
-   * @return the modification stamp for the source
+   * This method should be used rather than the method
+   * [Source.getModificationStamp] because contexts can have local overrides of
+   * the content of a source that the source is not aware of.
    */
   int getModificationStamp(Source source);
 
   /**
    * Return a fully resolved AST for a single compilation unit within the given library, or
    * `null` if the resolved AST is not already computed.
    *
    * @param unitSource the source of the compilation unit
    * @param library the library containing the compilation unit
    * @return a fully resolved AST for the compilation unit
@@ skipping 11632 matching lines @@
     if (element.id == _id) {
       result = element;
       throw new _ElementByIdFinderException();
     }
     super.visitElement(element);
   }
 }
 
 class _ElementByIdFinderException {
 }