I set up a simple flow with "All Conditions Are Met (AND)" with Field | Is Null | True. This should trigger whenever the lookup field is null. It triggers as it should but now I want to change it into a formula to accomplish the same thing:


Surprisingly, this does not work. However, if I change it slightly it works:


I remember that in other formulas you should now use ISBLANK() instead of ISNULL() - is this the case for flows as well? If so, can somebody point me to a source? But most importantly - why does the lookup field not work with both functions? If the new functions "only" adds support for text fields - why does it not work with a normal lookup field?

  • 2
    Our experience was that ISNULL is not reliable anywhere and you should always use ISBLANK instead. Can't cite documentation right now.
    – Phil W
    May 17, 2023 at 6:22

1 Answer 1


According to documentation, ISBLANK is the prefered function to utilize for all new formulas as it expands on previous functionality and will continue to be supported moving forward:

Use ISBLANK instead of ISNULL in new formulas. ISBLANK has the same functionality as ISNULL, but also supports text fields. Salesforce will continue to support ISNULL, so you do not need to change any existing formulas.

Please see the following link for more details: https://help.salesforce.com/s/articleView?id=sf.customize_functions_isblank.htm&type=5

  • Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference.
    – identigral
    May 17, 2023 at 17:31
  • 1
    Fair point @identigral. I have added quotes from the linked documentation and explanation.
    – DC-Fencer
    May 19, 2023 at 13:32

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