Hello! I’m not sure why is it not working with my addfilter node. Everything beforehand works fine. I just don’t know what is the issue causing it error.
What does the warning say?
Im not sure what it means
Im thinking something’s wrong with the value for ‘Mark’ and ‘Panel’. I simply just put a blank space " " to make it work, without putting any value was not working. The ‘description’ filter is working in revit but not the other two that has the filtertype “HasValue”
I am not behind a PC at the moment.
“ “ is a Space. Maybe try ““ instead?
It actually stays the same, nothing changes
Maybe this will get you somewhere. Have a look at first two search results.
So maybe use something else than HasValue for filtering Elements which have no value for that Parameter.
If that doesn’t resolve the issue then you have to wait for someone else who might have an idea.
There is no way, it works now! 
I changed my “HasValue” —> “GreaterThan” and keep the blank space the same. The link you sent was very helpful. Thank you!
Workaround:
To find a parameter with an empty value (or no value, or null), use the operator “equals,” and leave the value blank.
To find a parameter that has a value (is not null), use “is greater than,” and leave the value blank.
Mark my answer as Solution?
EDIT
Thanks. 