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 new ArrayList( derived );
		return new ArrayList( );
	}
	/**
	 * Returns the valid status of this element. Child elements need to
	 * overwrite this method to say in which condition they can be said valid or
	 * not.
	 * <p>
	 * for example, if a JDBCDataSource can not reach the server, then it's
	 * invalid.
	 * <p>
	 * UI needs this method to show different icon for each element in the user
	 * interface.
	 * 
	 * @return true if this element is valid, false otherwise.
	 */
	public boolean isValid( )
	{
		return isValid;
	}
	/**
	 * Sets whether the element is valid.
	 * 
	 * @param isValid
	 *            the valid to set
	 */
	public void setValid( boolean isValid )
	{
		this.isValid = isValid;
	}