# Parameter value Problem Dynamo after fill and clear (inside Revit)

**URL:** <https://forum.dynamobim.com/t/parameter-value-problem-dynamo-after-fill-and-clear-inside-revit/83591>\
**Category:** Revit\
**Tags:** dynamo\
**Created:** [November 29, 2022, 3:33pm UTC](https://forum.dynamobim.com/t/parameter-value-problem-dynamo-after-fill-and-clear-inside-revit/83591 "2022-11-29T15:33:50Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![bsJB9HQ](https://avatars.discourse-cdn.com/v4/letter/b/cdc98d/32.png) [@bsJB9HQ](https://forum.dynamobim.com/u/bsJB9HQ)\
**Post date:** [November 29, 2022, 3:33pm UTC](https://forum.dynamobim.com/t/parameter-value-problem-dynamo-after-fill-and-clear-inside-revit/83591/1 "2022-11-29T15:33:50Z")

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Hello, I have a parameter called “Beschreibung” if it’s never been described, dynamo returns null (which is correct) but when it’s filled in and the text is removed afterwards, it’s no longer null and that breaks my filters.

Is there a reason and a possibility that my filter can still work somehow?

If never filled out

 ![image](https://us1.discourse-cdn.com/flex022/uploads/dynamobim/original/3X/d/8/d8ba8368b454b70786ebe5e590ed34dee35297ef.png)

If filled in once and later cleared

 ![image](https://us1.discourse-cdn.com/flex022/uploads/dynamobim/original/3X/2/e/2e9ed5a0c30b629c74a7522105adb7a8b73bc44d.png)

Thanks for every help

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**Author:** ![Nick\_Boyts](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.dynamobim.com/nick_boyts/32/76313_2.png) [@Nick\_Boyts](https://forum.dynamobim.com/u/Nick_Boyts)\
**Post date:** [November 29, 2022, 3:41pm UTC](https://forum.dynamobim.com/t/parameter-value-problem-dynamo-after-fill-and-clear-inside-revit/83591/2 "2022-11-29T15:41:23Z")

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This is typical for many parameter types in Revit. Parameters will have no value (null) until they are filled out. After that, they can only be modified or cleared (empty value) but not reset to no value (null).

For string values (which can typically be cleared), this is easy enough to work around in Dynamo as you just need to make two checks instead of one. Check that the value is either null OR empty (`""`).

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**Author:** ![Draxl\_Andreas](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.dynamobim.com/draxl_andreas/32/145744_2.png) [@Draxl\_Andreas](https://forum.dynamobim.com/u/Draxl_Andreas)\
**Post date:** [November 29, 2022, 4:55pm UTC](https://forum.dynamobim.com/t/parameter-value-problem-dynamo-after-fill-and-clear-inside-revit/83591/3 "2022-11-29T16:55:31Z")

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@bsJB9HQ ,

emptyness is killing me… 😉 We use so called Optionsets f.e. “ND” (not defined) or “False” “0” as values… …when everybody knows you can handle the data!

KR

Andreas

 ![grafik](https://us1.discourse-cdn.com/flex022/uploads/dynamobim/original/3X/6/6/661d4510a2ad767e136b894632f1a88244576a8e.png)