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
}
	/**
	 * Returns the shared style referenced by this element. This method will try
	 * to resolve the style element if the value is un-resolved.
	 * <p>
	 * Part of: Style system.
	 * 
	 * @param module
	 *            module
	 * @return the shared style, or null if this element does not explicitly
	 *         reference a shared style.
	 */
	public StyleElement getStyle( Module module )
	{
		return null;
	}
	/**
	 * Returns the shared style referenced by this element. This method will not
	 * try to resolve the style element if the value is un-resolved.
	 * <p>
	 * Part of: Style system.
	 * 
	 * @return the shared style, or null if this element does not explicitly
	 *         reference a shared style, or the value is un-resolved
	 */
	public StyleElement getStyle( )
	{
		return null;
	}
	/**