Fixed possible null reference exception.

ICSharpCode.NRefactory.CSharp/Completion/CSharpCompletionEngineBase.cs

@@ -430,6 +430,7 @@ namespace ICSharpCode.NRefactory.CSharp.Completion
 			bool wrapInClass = memberLocation != new TextLocation (1, 1);
 			if (wrapInClass) {
 				var nodeAtLocation = Unit.GetNodeAt (memberLocation, n => n is TypeDeclaration || n is NamespaceDeclaration);
+				if (nodeAtLocation != null) {
 					foreach (var n in nodeAtLocation.AncestorsAndSelf) {
 						if (memberLocation == n.StartLocation) {
 							continue;
@@ -459,6 +460,7 @@ namespace ICSharpCode.NRefactory.CSharp.Completion
 						}
 					}
 				}
+			}
 			wrapper.Append(memberText);
 			wrapper.Append(continuation);
 			AppendMissingClosingBrackets(wrapper, memberText, appendSemicolon);