Ignore 'dynamic' and 'void' elements in the occurrences computer too.

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 0a87298567d81fb976d656cae04c0081037d7af8..64f4687e29d3e10d58aca05fe4d79cbaa45329ff 100644
--- a/pkg/analysis_server/lib/src/computer/computer_occurrences.dart
+++ b/pkg/analysis_server/lib/src/computer/computer_occurrences.dart
@@ -39,6 +39,9 @@ class DartUnitOccurrencesComputer {
   }
 
   void _addOccurrence(Element element, int offset) {
+    if (element == null || element == DynamicElementImpl.instance) {
+      return;
+    }
     element = _canonicalizeElement(element);
     List<int> offsets = _elementsOffsets[element];
     if (offsets == null) {