[NUI] Fix svace issue

diff --git a/src/Tizen.NUI.Components/Controls/ButtonGroup.cs b/src/Tizen.NUI.Components/Controls/ButtonGroup.cs
index 8c5bea7..9d59a09 100755 (executable)
--- a/src/Tizen.NUI.Components/Controls/ButtonGroup.cs
+++ b/src/Tizen.NUI.Components/Controls/ButtonGroup.cs
@@ -138,7 +138,10 @@ namespace Tizen.NUI.Components
             {
                 foreach (Button btn in btGroup.itemGroup)
                 {
-                    btn.OverlayImage.BackgroundColor = ((Selector<Color>)newValue).All;
+                    if (btn.OverlayImage != null)
+                    {
+                        btn.OverlayImage.BackgroundColor = ((Selector<Color>)newValue).All;
+                    }
                 }
                 btGroup.overLayBackgroundColorSelector = (Selector<Color>)newValue;
             }