Issue 23184. Fix for exception when 'async' is used outside of a function body.

pkg/analysis_server/lib/src/services/correction/fix_internal.dart

Index: pkg/analysis_server/lib/src/services/correction/fix_internal.dart
diff --git a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
index eb9c8357dd6c02c054fcb77e710e99eff051a1e7..d370589aad437702f6ca312663ca5c7d267e33a8 100644
--- a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
@@ -330,7 +330,7 @@ class FixProcessor {
     AstNode node = this.node;
     if (_isAwaitNode()) {
       FunctionBody body = node.getAncestor((n) => n is FunctionBody);
-      if (body.keyword == null) {
+      if (body != null && body.keyword == null) {
         _addReplaceEdit(rf.rangeStartLength(body, 0), 'async ');
         _addFix(DartFixKind.ADD_ASYNC, []);
         return true;