Bug 175664 [Mac] Unexpected internal exception occurs when invoke expression builder
Description: There are two problems: 1. "fx" button (Click this button to invoke Expression Builder) could not be displayed correctly, nothing displayed in the button. 2. Click on the button, an unexpected internal exception occurs. Version:2.2.0.v20070205 Steps to reproduce: 1.Insert a Data item to the layout. Click "fx" button to invoke the expression builder, although on Mac "fx" button could not display correctly. Error log: Argument cannot be null Plug-in Provider: Eclipse.org Plug-in Name: BIRT Designer UI Plug-in ID: org.eclipse.birt.report.designer.ui Error Code: Error.GUIException.invokedByUnexpectedException Error Message:Argument cannot be null
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/internal/ui/util/UIUtil.java
* @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
	 * 
	 * @return the width hint
	 */
	public static int getWidthHint( int wHint, Control c )
	{