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( );
	}
	/**
	 * Returns the slot within the container element that holds this element.
	 * 
	 * @return the container's slot in which this element appears
	 */
	public int getContainerSlot( )
	{
		return containerSlotID;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.core.IPropertySet#getObjectDefn()
	 */
	public IObjectDefn getObjectDefn( )
	{
		return getDefn( );
	}
	/**
	 * Returns the value of an element reference property as an element. Returns
	 * null if either the property is unset, or the reference is unresolved.
	 * 
	 * @param module
	 *            the module
	 * @param propName
	 *            the name of the element reference property to get
	 * @return the element referenced by the property