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
{
			return 0;
		}
		else if ( obj instanceof StructuredSelection )
		{
			return getObjectLength( ( (StructuredSelection) obj ).toArray( ) );
		}
		else if ( obj instanceof Object[] )
		{
			return ( (Object[]) obj ).length;
		}
		return 1;
	}
	/**
	 * Checks whether child's container exists in handle array
	 * 
	 * @param content
	 *            child handle
	 * @param handles
	 *            handle array
	 * @return if exists
	 */
	public static boolean checkContainerExists( Object content, Object[] handles )
	{
		content = unwrapToModel( content );
		DesignElementHandle child = null;
		if ( content instanceof SlotHandle )
		{
			child = ( (SlotHandle) content ).getElementHandle( );
		}