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Q156925: PRB: NULL and .NULL. Are Not Interchangeable in Properties

Article: Q156925
Product(s): Microsoft FoxPro
Version(s): WINDOWS:5.0,6.0
Operating System(s): 
Keyword(s): kbvfp500 kbvfp600
Last Modified: 14-DEC-1999

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 5.0, 6.0 
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SYMPTOMS
========

In Visual FoxPro 5.0, when assigning a null value to a property in the
Properties window, you need to use .NULL. instead of NULL. The values are not
interchangeable when used in a property in the Properties window.

CAUSE
=====

In the Properties window, you do not have to enter quotes to enter a string. The
text NULL entered without the quotes is interpreted as the string 'NULL' instead
of the actual .NULL. value.

WORKAROUND
==========

You need to enter the string as .NULL. in the Properties window.

STATUS
======

This behavior is by design.

MORE INFORMATION
================

At times, you may wonder why you can enter the following in the Command window
and get the expected result:

     X=NULL
     ?ISNULL(X)   <-- .T. is return

However, ISNULL() evaluates as .F. instead of .T. when a NULL value, without the
period on both ends, is assigned to a property in the Properties window.

Steps to Reproduce Behavior
---------------------------

1. Create a new form.

2. Create a new property named NullProperty.

3. In the Properties window, assign NULL to NullProperty property (that is,
  without periods before and after NULL).

4. Put the following in the form Init:

        ?ISNULL(THIS.NullProperty)

5. Run the form.

Visual FoxPro returns .F.

Additional query words: kbdse VFoxWin

======================================================================
Keywords          : kbvfp500 kbvfp600 
Technology        : kbVFPsearch kbAudDeveloper kbVFP500 kbVFP600
Version           : WINDOWS:5.0,6.0

=============================================================================

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