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
*            <code>DesignElementHandle</code>,<code>SlotHandle</code>
	 *            or <code>ReportElementModel</code>
	 * @param position
	 *            the position will be added
	 * @param commandName
	 * @param commandType
	 *            TYPE_CUT or TYPE_COPY
	 * @return if succeeding in operating data
	 */
	protected static boolean operateHandles( Object transferData,
			Object targetObj, int position, String commandName,
			String commandType )
	{
		ModuleHandle designHandle = SessionHandleAdapter.getInstance( )
				.getReportDesignHandle( );
		CommandStack stack = designHandle.getCommandStack( );
		try
		{
			stack.startTrans( commandName );
			CompoundCommand commands = new CompoundCommand( );
			if ( transferData instanceof StructuredSelection )
			{
				transferData = ( (StructuredSelection) transferData ).toArray( );
			}
			addCommandToCompound( transferData, targetObj, position,
					commandName, commandType, commands );
			commands.execute( );
			stack.commit( );
		}
		catch ( Exception e )