apiserver: Allow blank resource username
apiserver: Allow blank resource username

The username is sometimes not defined at source.

AdamIsrael/juju,bac/juju,alesstimec/juju,ericsnowcurrently/juju,bac/juju,alesstimec/juju,frankban/juju,alesstimec/juju,AdamIsrael/juju,mikemccracken/juju,anastasiamac/juju,alesstimec/juju,mikemccracken/juju,reedobrien/juju,anastasiamac/juju,waigani/juju,mjs/juju,bac/juju,mjs/juju,marcmolla/juju,reedobrien/juju,reedobrien/juju,anastasiamac/juju,alesstimec/juju,mjs/juju,ericsnowcurrently/juju,marcmolla/juju,ericsnowcurrently/juju,frankban/juju,mjs/juju,reedobrien/juju,mikemccracken/juju,reedobrien/juju,mjs/juju,bac/juju,bac/juju,waigani/juju,mjs/juju,ericsnowcurrently/juju,waigani/juju,anastasiamac/juju,mikemccracken/juju,anastasiamac/juju,AdamIsrael/juju,mikemccracken/juju,frankban/juju,mjs/juju,ericsnowcurrently/juju,frankban/juju,marcmolla/juju,marcmolla/juju,frankban/juju,AdamIsrael/juju,marcmolla/juju,waigani/juju