code: function(fieldName, value) {
                  var queryStringValue;
                  if (!this.hasRegisteredFilterField(fieldName)) {
                      this.registerFilterableField(fieldName, '');
                  }
                  this.filterableFields[fieldName].value = value;
                  if (_.isArray(value)) {
                      queryStringValue = value.join(',');
                  } else {
                      queryStringValue = value;
                  }
                  this.queryParams[fieldName] = function() {
                      return queryStringValue || null;
                  };
                  this.isStale = true;
              }
docs: Sets a filter field to a given value and marks the
  collection as stale.
  
  @param fieldName {string} querystring parameter name for the
  filterable field
  @param value {*} value for the filterable field