Referencing a Null Value in an Item Based on a LOV

LOVs have a null display value option and a null return value option. The null display value is the value the end user sees in the list indicating the no selection from the proper (non-null) values of the list will be made. When a user selects a null display value, the LOV's null return value is sent to the application when the page is submitted. If the developer has left the null return value unspecified (or empty), the actual value transmitted is not an empty string or an Oracle null, but the literal %null%. The application must be prepared to deal with this literal and treat is as the null selection.

Be aware of this behavior when writing code to evaluate submitted values. For example, suppose a page evaluates the submitted item P1_X and you need to use the PL/SQL expression replace(:P1_X,'%'||'null%',null) to prepare the item for permanent storage in session state or for passing to DML or other APIs.

To avoid problems, be aware of the appropriate way to code %null% in expressions that occur in page computations, processes, and validations. You must break up the string so that the application does not replace %null% with a null value in the page metadata when it is saved. Consider the following example:

'%'||'null%'