Bug 145520 Group name will not show up in group list if the group use default name and key expression has no value
Description: Group name will not show up in group list if key expression has no value. Steps to reproduce: 1. Insert a table into report, bind it to a data set 2. Switch to property editor -> groups 3. Click on add button to open new group dialog, then press ok button Expected result: A new group with default name will be added to group list Actual result: A new group is added to group list, but without group name. But when let group tab lost focus and get focus again, you can see the group name.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/ContentCommand.java
* @throws UserPropertyException
	 *             if an error occurs, but the operation should not fail under
	 *             normal conditions
	 */
	private void dropUserProperties( DesignElement obj )
			throws UserPropertyException
	{
		Collection props = obj.getUserProperties( );
		if ( props != null )
		{
			UserPropertyCommand propCmd = new UserPropertyCommand( module, obj );
			Iterator iter = props.iterator( );
			while ( iter.hasNext( ) )
			{
				UserPropertyDefn prop = (UserPropertyDefn) iter.next( );
				propCmd.dropUserProperty( prop.getName( ) );
			}
		}
	}
	/**
	 * Removes all the contents of the element. Removes all contents from all
	 * slots. Does the drop recursively.
	 * 
	 * @param obj
	 *            the element to clean up
	 * @throws SemanticException
	 *             if an error occurs, but the operation should not fail under
	 *             normal conditions
	 */
	private void removeContents( DesignElement obj ) throws SemanticException