Document all the cases where HoverInformation fields can be absent.

pkg/analysis_server/lib/src/generated_protocol.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 file has been automatically generated.  Please do not edit it manually.
 // To regenerate the file, use the script
 // "pkg/analysis_server/spec/generate_files".
 
 part of protocol;
 /**
@@ skipping 6439 matching lines @@
 
   /**
    * The length of the range of characters that encompases the cursor position
    * and has the same hover information as the cursor position.
    */
   int length;
 
   /**
    * The path to the defining compilation unit of the library in which the
    * referenced element is declared. This data is omitted if there is no
-   * referenced element.
+   * referenced element, or if the element is declared inside an HTML file.
    */
   String containingLibraryPath;
 
   /**
    * The name of the library in which the referenced element is declared. This
-   * data is omitted if there is no referenced element.
+   * data is omitted if there is no referenced element, or if the element is
+   * declared inside an HTML file.
    */
   String containingLibraryName;
 
   /**
    * The dartdoc associated with the referenced element. Other than the removal
    * of the comment delimiters, including leading asterisks in the case of a
    * block comment, the dartdoc is unprocessed markdown. This data is omitted
-   * if there is no referenced element.
+   * if there is no referenced element, or if the element has no dartdoc.
    */
   String dartdoc;
 
   /**
    * A human-readable description of the element being referenced. This data is
    * omitted if there is no referenced element.
    */
   String elementDescription;
 
   /**
@@ skipping 3278 matching lines @@
     return false;
   }
 
   @override
   int get hashCode {
     int hash = 0;
     hash = _JenkinsSmiHash.combine(hash, newName.hashCode);
     return _JenkinsSmiHash.finish(hash);
   }
 }