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 ( source instanceof StructuredSelection )
		{
			return cloneSource( ( (StructuredSelection) source ).toArray( ) );
		}
		if ( source instanceof ColumnHandle )
		{
			try
			{
				int columnNumber = HandleAdapterFactory.getInstance( )
						.getColumnHandleAdapter( source ).getColumnNumber( );
				Object parent = ( (ColumnHandle) source ).getContainer( );
				if ( parent instanceof TableHandle )
				{
					return ( (TableHandle) parent ).copyColumn( columnNumber );
				}
				else if ( parent instanceof GridHandle )
				{
					return ( (GridHandle) parent ).copyColumn( columnNumber );
				}
			}
			catch ( SemanticException e )
			{
				e.printStackTrace( );
			}
			return null;
		}
		if ( source instanceof DesignElementHandle )
		{
			IDesignElement copyElement = ( (DesignElementHandle) source )