Gets the id of the default domain.

    If the requests default domain is the same as DEFAULT_DOMAIN,
    return None.

def get_effective_domain_id(request):
    """Gets the id of the default domain.

    If the requests default domain is the same as DEFAULT_DOMAIN,
    return None.
    """
    default_domain = get_default_domain(request)
    domain_id = default_domain.get('id')
    domain_name = default_domain.get('name')
    return None if domain_name == DEFAULT_DOMAIN else domain_id