XEP-0077 Registration must return <not-acceptable/> if username or password are unspecified.
Description
From XEP-0077:
If the requesting entity does not provide all of the requested information during registration [7] then the server or service MUST return a <not-acceptable/> error to the requesting entity.
Currently an <internal-server-error/> is returned instead.
Environment
None
Acceptance Test - Entry
None
