Bug 163018 An error extension will lead the report contain chart can't be opened and can not new a report.
Details: An error extension will lead the report contain chart can't open In org.eclipse.birt.report.tests.model has an error extension. When run the birt use workbenck, the report contain chart can't be opened and it can not new a report.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/metadata/ElementDefn.java
if ( slots == null )
			return;
		for ( int i = 0; i < slots.size( ); i++ )
		{
			SlotDefn slot = (SlotDefn) slots.get( i );
			slot.setSlotID( i );
			slot.build( );
		}
	}
	/**
	 * Returns a list of the localized property group names defined by this
	 * element and its parents.
	 * <p>
	 * The UI uses property groups to organize properties within the generic
	 * property sheet.
	 * 
	 * @return The list of group names. If there is no groups defined on the
	 *         element, the list will has no content.
	 */
	public List getGroupNames( )
	{
		
		ArrayList groupNames = new ArrayList( );
		Iterator iter = getProperties( ).iterator( );
		while ( iter.hasNext( ) )
		{
			SystemPropertyDefn prop = (SystemPropertyDefn) iter.next( );
			String groupName = prop.getGroupName( );
			if ( groupName != null && !groupNames.contains( groupName ) )
			{