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
/**
	 * Drops source data
	 * 
	 * @param source
	 *            source to drop
	 */
	public static void dropSource( Object source )
	{
		DeleteCommand command = new DeleteCommand( source );
		if ( command.canExecute( ) )
			command.execute( );
	}
	/**
	 * Gets handle of target
	 * 
	 * @param target
	 * @return handle of target
	 */
	public static DesignElementHandle getDesignElementHandle( Object target )
	{
		target = unwrapToModel( target );
		if ( target instanceof DesignElementHandle )
		{
			return (DesignElementHandle) target;
		}
		else if ( target instanceof SlotHandle )
		{
			return ( (SlotHandle) target ).getElementHandle( );
		}
		return null;