code: function getModelView (modelViewName) {
      // if name is not passed then return all
      if (!modelViewName) {
          return immutableCoreModelView.modelViews
      }
      // if model view is passed then model view must be defined
      assert.ok(immutableCoreModelView.modelViews[modelViewName], 'model view '+modelViewName+' not found')
      // return model view
      return immutableCoreModelView.modelViews[modelViewName]
  }
docs: @function getModelView
  
  if modelViewName passed return model view by name. otherwise return object
  with all global model views indexed by name. if name is passed and model
  view is not defined error will be thrown.
  
  @param {string|undefined} modelViewName
  
  @returns {ImmutableCoreModelView|object}