Bug 143898 [smoke][regression]Chart cannot be extended from library file
Description: Chart cannot be extended from library file Step to reproduce: 1. New a library and insert chart, publish it. 2. New a report, drag data source, dataset and chart to Layout from library 3. Save the report. Result: GUIException: caused by java.lang.reflect. invocation targetexception
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/validators/ExtensionValidator.java
* @return error list, each of which is the instance of
	 *         <code>SemanticException</code>.
	 */
	public List validate( Module module, DesignElement element )
	{
		if ( !( element instanceof ExtendedItem ) )
			return Collections.EMPTY_LIST;
		return doValidate( module, (ExtendedItem) element );
	}
	private List doValidate( Module module, ExtendedItem toValidate )
	{
		List list = new ArrayList( );
		if ( toValidate.getExtendedElement( ) == null )
		{
			try
			{
				toValidate.initializeReportItem( module );		
			}
			catch ( ExtendedElementException e )
			{
				return list;
			}
		}
		
		List exceptions = toValidate.getExtendedElement( ).validate( );
		if ( exceptions != null )
			list.addAll( exceptions );
		return list;
	}
}