[NUI] DragAndDrop: fix svace error

diff --git a/src/Tizen.NUI/src/public/DragAndDrop/DragAndDrop.cs b/src/Tizen.NUI/src/public/DragAndDrop/DragAndDrop.cs
index 9dc5bf4..e824e4e 100755 (executable)
--- a/src/Tizen.NUI/src/public/DragAndDrop/DragAndDrop.cs
+++ b/src/Tizen.NUI/src/public/DragAndDrop/DragAndDrop.cs
@@ -73,7 +73,7 @@ namespace Tizen.NUI
                 throw new ArgumentNullException(nameof(shadowView));
             }
 
-            if (mDragWindow != null)
+            if (null == mDragWindow)
             {
                 mDragWindow = new Window("DragWindow", new Rectangle(-shadowWidth, -shadowHeight, shadowWidth, shadowHeight), true)
                 {