Raising command to "change" value to the same value doesn't produce event nor exception

[maraf]

A client awaiting such operation doesn't get a response.
None of the aggregate operations handle it, except for the check if the aggregate root is deleted.
Not doing anything breaks the idea of "command either produce event(s) or exception".
"Process once" of command contract should be handled by the infrastructure (not firing command for processing once it was processed).