Make findElementReferences' "id" result optional.

pkg/analysis_server/doc/api.html

Index: pkg/analysis_server/doc/api.html
diff --git a/pkg/analysis_server/doc/api.html b/pkg/analysis_server/doc/api.html
index 330806b8d2d74caf17d1a6e603f50484200ab143..4a4f235bd2b377dd40cf7e8c89640188f3e488fe 100644
--- a/pkg/analysis_server/doc/api.html
+++ b/pkg/analysis_server/doc/api.html
@@ -994,7 +994,7 @@ dt.typeDefinition {
   "<b>id</b>": String
   "error": <span style="color:#999999">optional</span> <a href="#type_RequestError">RequestError</a>
   "result": {
-    "<b>id</b>": <a href="#type_SearchId">SearchId</a>
+    "<b>id</b>": <span style="color:#999999">optional</span> <a href="#type_SearchId">SearchId</a>
     "<b>element</b>": <span style="color:#999999">optional</span> <a href="#type_Element">Element</a>
   }
 }</pre></div>
@@ -1027,12 +1027,17 @@ dt.typeDefinition {
               True if potential matches are to be included in the
               results.
             </p>
-          </dd></dl><h4>Returns</h4><dl><dt class="field"><b><i>id ( <a href="#type_SearchId">SearchId</a> )</i></b></dt><dd>
+          </dd></dl><h4>Returns</h4><dl><dt class="field"><b><i>id ( <span style="color:#999999">optional</span> <a href="#type_SearchId">SearchId</a> )</i></b></dt><dd>
             
             <p>
               The identifier used to associate results with this
               search request.
             </p>
+            <p>
+              If no element was found at the given location, this
+              field will be absent, and no results will be reported
+              via the search.results notification.
+            </p>
           </dd><dt class="field"><b><i>element ( <span style="color:#999999">optional</span> <a href="#type_Element">Element</a> )</i></b></dt><dd>
             
             <p>