Bug 146159 [Regression]Changing font operation doesn't work other than the first time
Description: The first time changing operation can work well. However, Change it again, it won't work. Steps: 1.Insert lable/text to layout or master page 2.Change the font from serif to cursive, it works well 3.Change the font again Result: The action doesn't work Additional infor: build number:200606080632
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/internal/ui/util/UIUtil.java
* 
	 * @param string
	 *            the string to convert
	 * @param trim
	 *            specify if the string needs to be trimmed
	 * @return the string, or null for an empty string
	 */
	public static String convertToModelString( String string, boolean trim )
	{
		if ( string == null )
		{
			return null;
		}
		if ( trim )
		{
			string = string.trim( );
		}
		if ( string.length( ) == 0 )
		{
			string = null; 
		}
		return string;
	}
	/**
	 * Returns the width hint for the given control.
	 * 
	 * @param wHint
	 *            the width hint
	 * @param c
	 *            the control