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
}
	/**
	 * Unwraps the object to model
	 * 
	 * @param obj
	 *            object which may be wrapped, such as
	 *            <code>ReportElementModel</code>, <code>ListBandProxy</code>
	 * @return model object
	 */
	public static Object unwrapToModel( Object obj )
	{
		if ( obj instanceof ReportElementModel )
		{
			return ( (ReportElementModel) obj ).getSlotHandle( );
		}
		if ( obj instanceof ListBandProxy )
		{
			return ( (ListBandProxy) obj ).getSlotHandle( );
		}
		return obj;
	}
	/**
	 * Gets the length of elements in object
	 * 
	 * @param obj
	 * @return the length of elements in object
	 */
	public static int getObjectLength( Object obj )
	{
		if ( obj == null )