Process builder that makes a cross-object reference will fail when the foreign key (i.e. relationship field) the reference depends on is not populated.

In this we will show if you got the below error in Process Builder then how you will you tackle them.
We are taking two object i.e Case and Work Order which will check for the some picklist value

Process Builder Error 'The flow failed to access the value because it hasn't been set or assigned'


CASE([WorkOrder].Case.Type,"Picklist Value",0,1)=1


Post Content Credit : I must thanks to my friend Sai Parjanya for this article