Different Input Models for Different Use Cases

We might be tempted to use the same input model for different use cases. Let's consider the use cases "Register Account" and "Update Account Details." Both will initially need almost the same input, namely some account details such as a description of the account.

The difference is that the "Update Account Details" use case also needs the ID of the account to be able to update that specific account. And the "Register Account" use case might need the ID of the owner, so that it can assign it to him or her. So, if we share the same input model between both use cases, we'd have to allow a null account ID to be passed into the "Update Account Details" use case and a null owner ID to be passed into the "Register Account" use case.

Allowing null as a valid state of a field in our immutable command object is a code smell by itself. But more importantly, how are we handling input validation...