Fix null ref error in get_effective_instance_user
Fix null ref error in get_effective_instance_user

The function was assuming that the argument was not None.

clever-crow-consulting/otm-core,maurizi/otm-core,clever-crow-consulting/otm-core,clever-crow-consulting/otm-core,RickMohr/otm-core,RickMohr/otm-core,RickMohr/otm-core,recklessromeo/otm-core,recklessromeo/otm-core,recklessromeo/otm-core,maurizi/otm-core,maurizi/otm-core,clever-crow-consulting/otm-core,RickMohr/otm-core,recklessromeo/otm-core,maurizi/otm-core