# Empty 'From Room' value causing error ...?

**URL:** <https://forum.dynamobim.com/t/empty-from-room-value-causing-error/11097>\
**Category:** Revit\
**Created:** [April 17, 2017, 3:35pm UTC](https://forum.dynamobim.com/t/empty-from-room-value-causing-error/11097 "2017-04-17T15:35:53Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![thomas\_garvin](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.dynamobim.com/thomas_garvin/32/24425_2.png) [@thomas\_garvin](https://forum.dynamobim.com/u/thomas_garvin)\
**Post date:** [April 17, 2017, 3:35pm UTC](https://forum.dynamobim.com/t/empty-from-room-value-causing-error/11097/1 "2017-04-17T15:35:53Z")

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I’m trying to extract Door-Room information from Revit to Excel. I’m getting an error ‘Warning: Internal error, please report: Dereferencing a non-pointer’ from the ‘fromRoom’ ‘Room.Number’ & ‘Room.Name’. I think it maybe because the external doors don’t have a Room from (as it’s working fine with to Room).

 ![](https://us1.discourse-cdn.com/flex022/uploads/dynamobim/original/3X/a/a/aafe6a466aa1a9bb72678917f3a5838a3a514075.JPG)  
Can anybody help? I’m fairly new to Dynamo and I need this in a panic for my final year college project. I suspect I need to put an ‘if’ condition in to tell it to replace an empty value with a specified value…?? How would I do that though?

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**Author:** ![Kulkul](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.dynamobim.com/kulkul/32/49801_2.png) [@Kulkul](https://forum.dynamobim.com/u/Kulkul)\
**Post date:** [April 17, 2017, 5:05pm UTC](https://forum.dynamobim.com/t/empty-from-room-value-causing-error/11097/2 "2017-04-17T17:05:36Z")

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Hi @thomas_garvin

That’s because you have null values in your list. You can fix this issue by replacing null values by a string “None”. See below.

 ![](https://us1.discourse-cdn.com/flex022/uploads/dynamobim/original/3X/1/2/121215c69035e3e9326eabe64b20307c85b671a8.png)

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**Author:** ![thomas\_garvin](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.dynamobim.com/thomas_garvin/32/24425_2.png) [@thomas\_garvin](https://forum.dynamobim.com/u/thomas_garvin)\
**Post date:** [April 17, 2017, 5:54pm UTC](https://forum.dynamobim.com/t/empty-from-room-value-causing-error/11097/3 "2017-04-17T17:54:44Z")

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Kulkul thank you very much for that

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<div class="post-metadata">

**Author:** ![thomas\_garvin](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.dynamobim.com/thomas_garvin/32/24425_2.png) [@thomas\_garvin](https://forum.dynamobim.com/u/thomas_garvin)\
**Post date:** [April 17, 2017, 6:49pm UTC](https://forum.dynamobim.com/t/empty-from-room-value-causing-error/11097/4 "2017-04-17T18:49:10Z")

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Kulkul,  
I wonder could you help me out again? I haven’t been able to pull out parameter values from the ‘ReplaceByCondition’ node. I’ve tried various methods including Element.GetParameterValueByName but to no avail, it just reports a function.