Issue 21238. Fix for NPE in occurrences computer when FieldFormalParameterElement references unreso…

pkg/analysis_server/lib/src/computer/computer_occurrences.dart

Index: pkg/analysis_server/lib/src/computer/computer_occurrences.dart
diff --git a/pkg/analysis_server/lib/src/computer/computer_occurrences.dart b/pkg/analysis_server/lib/src/computer/computer_occurrences.dart
index a4d53e0bfcc9de4d58737a556bbab110cac8a1a0..d1c941f9cf27aa1427ed6b7a3a20101d8b1658a1 100644
--- a/pkg/analysis_server/lib/src/computer/computer_occurrences.dart
+++ b/pkg/analysis_server/lib/src/computer/computer_occurrences.dart
@@ -37,10 +37,10 @@ class DartUnitOccurrencesComputer {
   }
 
   void _addOccurrence(Element element, int offset) {
+    element = _canonicalizeElement(element);
     if (element == null || element == DynamicElementImpl.instance) {
       return;
     }
-    element = _canonicalizeElement(element);
     List<int> offsets = _elementsOffsets[element];
     if (offsets == null) {
       offsets = <int>[];