Bug 152430 Key can modify to empty string
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/PropertyCommand.java
if ( struct.isReferencable( ) )
			adjustReferenceClients( (ReferencableStructure) struct );
		PropertyListRecord record = new PropertyListRecord( element, structRef,
				list );
		stack.execute( record );
		stack.commit( );
	}
	/**
	 * Adjusts references to a structure that is to be deleted. The structure to
	 * be deleted is one that has references in the form of structure reference
	 * properties on other elements. These other elements, called "clients",
	 * each contain a property of type structure reference and that property
	 * refers to this structure. Each reference is recorded with a "back
	 * pointer" from the referenced structure to the client. That back pointer
	 * has both a pointer to the client element, and the property within that
	 * element that holds the reference. The reference property is unresolved.
	 * 
	 * @param struct
	 *            the structure to be deleted
	 */
	private void adjustReferenceClients( ReferencableStructure struct )
	{
		assert struct != null;
		if ( !struct.hasReferences( ) )
			return;
		List clients = new ArrayList( struct.getClientList( ) );
		Iterator iter = clients.iterator( );
		while ( iter.hasNext( ) )
		{
			BackRef ref = (BackRef) iter.next( );