code: function(filterFieldName) {
                  var val = this.getActiveFilterFields(true)[filterFieldName];
                  return (_.isNull(val) || _.isUndefined(val)) ? null : val;
              }
docs: Gets the value of the given filter field.
  
  @returns {String} the current value of the requested filter
  field.  null means that the filter field is not active.