Yeah, I agree to that, Mike.
In addition: I've experience that kind of error, when a custom ABAP OO Workflow-Class is returning INITIAL on the bi_persistent~find_by_lpor() call, when the given lpor-instID was INITIAL.
Becaus the Workflow Builder will instantiate all container elements, used in operations or expressions with a "null"-instance to dummy-call functional method, just to see, if they work.
At the beginning of my ABAP Class-experiences I had used the CX_BO_ERROR and and existence_check() method to have a pattern similar to the BOR Object types implemented, but it turned out to screw up the things, which is kinda pitty though.
However, @Harsha, it is very likely that the Workflow builder got an initial reference from one of the ABAP Classes that were used in a Container. You may also find that out through the call-history (as Mike was suggesting), as well as rummaging through break-points of the CONSTRUCTORS of any possible ABAP Class, affected and used by that Workflow pattern.
Best wishes
Florin