Bug 124620 Referenced Parameter icon should be invalid if the parameter in library is deleted
Description: Referenced parameter icon should be invalid if the source parameter in library is deleted. Steps to reproduce: 1.Create a library. Insert a report scalar parameter. 2.Create a report, use the above library. In the library explorer, pull the parameter to the data explorer view of report. 3.Open the library file, delete the parameter. Then reopen the report design file, the icon of parameter seems nothing happened. But if those operations happened in dataset, the icon of dataset in the report will be invalid. It is acceptable. Expected Result: The icon of referenced parameter should be invalid.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
return getSessionDefaultValue( module, prop );
	}
	/**
	 * Gets the session default value of the specified property if it is style
	 * property.
	 * 
	 * @param module
	 *            module
	 * @param prop
	 *            definition of the property to get
	 * @return The session default property value, or null if no default value
	 *         is set.
	 */
	private Object getSessionDefaultValue( Module module,
			ElementPropertyDefn prop )
	{
		if ( prop.isStyleProperty( ) )
		{
			
			return module.session.getDefaultValue( prop.getName( ) );
		}
		return null;
	}
	/**
	 * Gets selector of the given slot of this element. The selector is kind of
	 * predefined style, and its style property value can be applied on contents
	 * of the given slot of this element depending on whether property can be
	 * inherited.
	 *