My use-case is the upsert of an entity identified by two values. I have an update route with these two values as route parameters, and a create route with only one. In that case the second value is null but the EntityValueResolver will still call the repository’s find method, resulting in a MissingIdentifierField exception:

The identifier [VALUE] is missing for a query of [ENTITY]

This PR makes the EntityValueResolver return null in this case, like when a scalar ID is null.