Bug 124600 delete Grid Column causes NPE thrown out in error log
steps to reproduce: - insert a 3*3 grid - delete grid columns one by one expected behavior: - these operations should completed without any error. actual behavior: - after i deleted the 3rd column, NPE was thrown out in error log.
UI/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/util/DNDUtil.java
}
			if ( targetHandle.getClass( ).equals( childHandle.getClass( ) ) )
			{
				
				return CONTAIN_PARENT;
			}
			return targetHandle.getContainer( ).canContain(
					targetHandle.getContainerSlotHandle( ).getSlotID( ),
					childHandle ) ? CONTAIN_PARENT : CONTAIN_NO;
		}
		return CONTAIN_NO;
	}
	/**
	 * Validates target can contain more elements
	 * 
	 * @param targetObj
	 *            target
	 * @param length
	 *            the length of elements in source.If do not add to target, set
	 *            zero
	 * @return whether target can contain more elements
	 */
	public static boolean handleValidateTargetCanContainMore( Object targetObj,
			int length )
	{
		if ( targetObj == null || length < 0 )
		{
			return false;
		}
		if ( targetObj instanceof StructuredSelection )