Is it possible to set a picklist to blank using Process Builder. From what we can tell it just gives you an option of any of the picklist values, but wont let you save the value as blank?
Is there some other way to clear the value of a picklist field like that?
You can set a lookup field to blank or null by entering in 15 zeros
Have you queried it from the sObject variable you passed in? Initially, only the sObject's values are available... So, if you want to access it's parent sObject's values, you'll need to query them first. This is the same behavior you'd experience in a trigger.
To resolve this, I recommend using a Quick Lookup item in your flow.
Best Answer
I'm a bit late to the party, but for future reference there's a $GlobalConstant.Null field that can be used for this: