[NUI] Fix warning by checking null argument in LayoutGroup

Like other APIs in LayoutGroup, exception should occur if LayoutItem
argument "child" is null.

diff --git a/src/Tizen.NUI/src/public/Layouting/LayoutGroup.cs b/src/Tizen.NUI/src/public/Layouting/LayoutGroup.cs
index 420d0f5..5c972ce 100755 (executable)
--- a/src/Tizen.NUI/src/public/Layouting/LayoutGroup.cs
+++ b/src/Tizen.NUI/src/public/Layouting/LayoutGroup.cs
@@ -626,9 +626,15 @@ namespace Tizen.NUI
         /// <param name="child">The child to measure.</param>
         /// <param name="parentWidthMeasureSpec">The width requirements for this view.</param>
         /// <param name="parentHeightMeasureSpec">The height requirements for this view.</param>
+        /// <exception cref="ArgumentNullException"> Thrown when child is null. </exception>
         [EditorBrowsable(EditorBrowsableState.Never)]
         protected void MeasureChildWithoutPadding(LayoutItem child, MeasureSpecification parentWidthMeasureSpec, MeasureSpecification parentHeightMeasureSpec)
         {
+            if (null == child)
+            {
+                throw new ArgumentNullException(nameof(child));
+            }
+
             View childOwner = child.Owner;
 
             MeasureSpecification childWidthMeasureSpec = GetChildMeasureSpecification(