NAME: SPD_UI_COMBOBOX PURPOSE: IDL combobox doesn't actually support null strings('') as entries in the combobox. Entering a null string will generate an error that halts execution. This is a simple wrapper compound widget to fix this problem by making the box appear empty when it is not. CALLING SEQUENCE: Result = SPD_UI_COMBOBOX KEYWORD PARAMETERS: Exactly the same as normal combobox EVENT STRUCTURE: The same as normal combobox, with the exception that the event structure is called 'SPD_UI_COMBOBOX'