Issue 21883. Add checks if type parameters can be used.

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

Index: pkg/analysis_server/lib/src/services/correction/assist_internal.dart
diff --git a/pkg/analysis_server/lib/src/services/correction/assist_internal.dart b/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
index 2fcc8c3d0150088383cac95dc870b6375185cd13..84eeeac1a476b25350b5bdecc42563b47b4c9f8d 100644
--- a/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
@@ -236,6 +236,7 @@ class AssistProcessor {
     String typeSource;
     DartType type = declaredIdentifier.identifier.bestType;
     if (type is InterfaceType || type is FunctionType) {
+      _configureTargetLocation(node);
       Set<LibraryElement> librariesToImport = new Set<LibraryElement>();
       typeSource = utils.getTypeSource(type, librariesToImport);
       _addLibraryImports(librariesToImport);
@@ -290,6 +291,7 @@ class AssistProcessor {
     // prepare type source
     String typeSource;
     if (type is InterfaceType || type is FunctionType) {
+      _configureTargetLocation(node);
       Set<LibraryElement> librariesToImport = new Set<LibraryElement>();
       typeSource = utils.getTypeSource(type, librariesToImport);
       _addLibraryImports(librariesToImport);
@@ -1623,6 +1625,20 @@ class AssistProcessor {
   }
 
   /**
+   * Configures [utils] using given [target].
+   */
+  void _configureTargetLocation(Object target) {
+    utils.targetClassElement = null;
+    if (target is AstNode) {
+      ClassDeclaration targetClassDeclaration =
+          target.getAncestor((node) => node is ClassDeclaration);
+      if (targetClassDeclaration != null) {
+        utils.targetClassElement = targetClassDeclaration.element;
+      }
+    }
+  }
+
+  /**
    * Returns an existing or just added [LinkedEditGroup] with [groupId].
    */
   LinkedEditGroup _getLinkedPosition(String groupId) {