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 null;
	}
	/**
	 * 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.
	 */
	public Object getProperty( Module module, PropertyDefn prop )
	{
		return getProperty( module, (ElementPropertyDefn) prop );
	}
	/**
	 * Returns whether this element is a style. While this information could be
	 * computed from meta-data, it is computed here for performance.
	 * 
	 * @return true if this is a style element, false otherwise.
	 */
	public boolean isStyle( )
	{
		return false;
	}
	/**
	 * Gets a property value given its internal name. This version checks only
	 * this one object. That is, it gets the "local" property value. The
	 * property name must also be valid for this object. The name can be a