Bug 138562 Splite extendsexcpetion to seperate sub class
The suggestion is Parent invalid Cycle extends Different type extends Not top level extends
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
* of the given slot of this element depending on whether property can be
	 * inherited.
	 * 
	 * @param slotID
	 *            slot id
	 * @return the selector of the given slot of this element.
	 */
	public String getSelector( int slotID )
	{
		ElementDefn defn = (ElementDefn) getDefn( );
		SlotDefn slotDefn = (SlotDefn) defn.getSlot( slotID );
		if ( slotDefn == null )
		{
			return null;
		}
		String slotSelector = slotDefn.getSelector( );
		if ( StringUtil.isBlank( slotSelector ) )
		{
			return null;
		}
		return slotSelector;
	}
	/**
	 * Returns the property value.
	 * 
	 * @param module
	 *            the module
	 * @param prop
	 *            the definition of property
	 * @return the property value, or null if no value is set.