docs: function getModel (app, name, Model) {
    const mongooseClient = app.get('mongoose');
    assert(mongooseClient, 'mongoose client not set by app');
    const modelNames = mongooseClient.modelNames();
    if (modelNames.includes(name)) {
      return mongooseClient.model(name);
    } else {
      assert(Model && typeof Model === 'function', 'Model function not privided.');
      return Model(app, name);
    }
  }