Check that target of a new constructor is a ClassDeclaration.

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 a33d280fe75cd346087c593f82cef1cadc3ab2d0..3fdd5f9a3db8a3b7a43e2afc1012365455acbf5e 100644
--- a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
@@ -700,10 +700,14 @@ class FixProcessor {
       return;
     }
     ClassElement targetElement = constructorElement.enclosingElement;
-    String targetFile = targetElement.source.fullName;
-    ClassDeclaration targetClass = getParsedClassElementNode(targetElement);
+    // prepare location for a new constructor
+    AstNode targetTypeNode = getParsedClassElementNode(targetElement);
+    if (targetTypeNode is! ClassDeclaration) {
+      return;
+    }
     _ConstructorLocation targetLocation =
-        _prepareNewConstructorLocation(targetClass);
+        _prepareNewConstructorLocation(targetTypeNode);
+    String targetFile = targetElement.source.fullName;
     // build method source
     SourceBuilder sb = new SourceBuilder(targetFile, targetLocation.offset);
     {
@@ -753,11 +757,15 @@ class FixProcessor {
     if (targetType is! InterfaceType) {
       return;
     }
+    // prepare location for a new constructor
     ClassElement targetElement = targetType.element as ClassElement;
-    String targetFile = targetElement.source.fullName;
-    ClassDeclaration targetClass = getParsedClassElementNode(targetElement);
+    AstNode targetTypeNode = getParsedClassElementNode(targetElement);
+    if (targetTypeNode is! ClassDeclaration) {
+      return;
+    }
     _ConstructorLocation targetLocation =
-        _prepareNewConstructorLocation(targetClass);
+        _prepareNewConstructorLocation(targetTypeNode);
+    String targetFile = targetElement.source.fullName;
     // build method source
     SourceBuilder sb = new SourceBuilder(targetFile, targetLocation.offset);
     {