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/metadata/ExtendsPropertyType.java
*         the target element.
	 */
	public Object validateValue( Module module, PropertyDefn defn, Object value )
			throws PropertyValueException
	{
		if ( value == null )
			return null;
		
		
		if ( value instanceof String )
		{
			String name = StringUtil.trimString( (String) value );
			if ( name == null )
			{
				logger.log( Level.SEVERE,
						"The value of the extends property is an empty string" ); 
				return null;
			}
			
			return validateStringValue( module, defn, (String) value );
		}
		if ( value instanceof DesignElement )
		{
			
			return validateElementValue( module, defn, (DesignElement) value );
		}
		
		logger.log( Level.SEVERE,
				"The value of the extends property is not a valid type " ); 
		throw new PropertyValueException( value,