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
/**
	 * Reports whether the given slot can contain elements of the given type.
	 * 
	 * @param slot
	 *            The slot to check.
	 * @param type
	 *            The element type to check.
	 * @return True if the slot can contain that element type, false if the
	 *         element is not a container, if the slot does not exist, or if the
	 *         slot can't contain that type of element.
	 */
	public boolean canContain( int slot, IElementDefn type )
	{
		if ( slots == null )
			return false;
		if ( slot < 0 || slot > slots.size( ) - 1 )
			return false;
		return ( (SlotDefn) slots.get( slot ) ).canContain( type );
	}
	/**
	 * Determines if the given element type is a kind of this type. It is if
	 * either the given type is the same as this one, or if the given type
	 * derives from this type.
	 * 
	 * @param type
	 *            The element type to check.
	 * @return True if it is a kind of this element, false otherwise.
	 */
	public boolean isKindOf( IElementDefn type )
	{