Issue 23568. Fix for NPE in index when unresolved field formal parameter.

pkg/analysis_server/test/services/index/dart_index_contributor_test.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.
 
 library test.services.src.index.dart_index_contributor;
 
 import 'package:analysis_server/analysis/index/index_core.dart';
 import 'package:analysis_server/src/services/index/index.dart';
 import 'package:analysis_server/src/services/index/index_contributor.dart';
 import 'package:analysis_server/src/services/index/index_store.dart';
@@ skipping 61 matching lines @@
             LocationImpl location) {
       recordedRelations
           .add(new RecordedRelation(indexable, relationship, location));
     });
     when(store.recordTopLevelDeclaration(anyObject))
         .thenInvoke((Element element) {
       recordedTopElements.add(element);
     });
   }
 
+  void test_bad_unresolvedFieldFormalParameter() {
+    verifyNoTestUnitErrors = false;
+    _indexTestUnit('''
+class Test {
+  final field;
+  Test(this.fie);
+}''');
+  }
+
   void test_definesClass() {
     _indexTestUnit('class A {}');
     // prepare elements
     ClassElement classElement = findElement("A");
     // verify
     _assertDefinesTopLevelElement(classElement);
   }
 
   void test_definesClassAlias() {
     _indexTestUnit('''
@@ skipping 1464 matching lines @@
 
   RecordedRelation(this.indexable, this.relationship, this.location);
 
   @override
   String toString() {
     return 'RecordedRelation(indexable=$indexable; relationship=$relationship; '
         'location=$location; flags=' '${location.isQualified ? "Q" : ""}'
         '${location.isResolved ? "R" : ""})';
   }
 }