def self.billing(model = nil, alt_object: nil, credentials: nil, model_version: "V2018_03_01_preview")
        require 'azure_mgmt_billing'

        if model and model.is_a?(Symbol)
          return Object.const_get("Azure").const_get("Billing").const_get("Mgmt").const_get(model_version).const_get("Models").const_get(model)