We have a VSI that does an Operation match that also has a match script to check the values of SSN, FirstName, and LastName. If all 3 match, we return true and return the response for that transaction. If the match is false, and all other transactions return false, then we return the Meta response which has an assertion to go to the live service.
There is a request argument called MiddleName which we have set to Anything in the comparison operator. If the request passes in a null value, it appears that the request is failing over to the live service. If a MiddleName value exists, it is hitting the virtual service. We know this because passing in a null is returning a DateOfBirth = 3/25/1998 for a specific transaction whereas when a MiddleName value is passed it returns 1/1/1960 for the DateOfBirth which is what we are expecting.
So why in an Operation match in which an argument is set to Anything and the match script doesn't care about that argument does it appear to be failing when a null is passed?