Improve code generation for 'bottom' and 'dynamic' arguments.

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 05e1e61f7e34dfd08e0dca909e3654f158f0eebf..af4e0464be7913581cd83fec15208be13ba9a566 100644
--- a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
@@ -1520,13 +1520,13 @@ class FixProcessor {
       Set<LibraryElement> librariesToImport = new Set<LibraryElement>();
       // TODO(scheglov) use librariesToImport
       String typeSource = utils.getTypeSource(type, librariesToImport);
-      {
+      if (typeSource != null) {
         sb.startPosition('TYPE$i');
         sb.append(typeSource);
         _addSuperTypeProposals(sb, new Set(), type);
         sb.endPosition();
+        sb.append(' ');
       }
-      sb.append(' ');
       // append parameter name
       {
         List<String> suggestions =