Handle null element in completion (issue 27461)

pkg/analysis_server/lib/src/services/completion/dart/suggestion_builder.dart

Index: pkg/analysis_server/lib/src/services/completion/dart/suggestion_builder.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/suggestion_builder.dart b/pkg/analysis_server/lib/src/services/completion/dart/suggestion_builder.dart
index 2a537bf072ce120e426fd1e2c20807a13ac1aed6..a57319a6dbce03a064a77ff7500771b04d3764b1 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/suggestion_builder.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/suggestion_builder.dart
@@ -29,6 +29,9 @@ CompletionSuggestion createSuggestion(Element element,
     CompletionSuggestionKind kind: CompletionSuggestionKind.INVOCATION,
     int relevance: DART_RELEVANCE_DEFAULT,
     Source importForSource}) {
+  if (element == null) {
+    return null;
+  }
   if (element is ExecutableElement && element.isOperator) {
     // Do not include operators in suggestions
     return null;