code: function validatorRadio(fieldValue, fieldDefinition, previousFieldValues, cb) {
        if (typeof(fieldValue) !== "string") {
          return cb(new Error("Expected submission to be string but got " + typeof(fieldValue)));
        }
  
        //Check value exists in the field definition
        if (!fieldDefinition.fieldOptions.definition.options) {
          return cb(new Error("No options exist for field " + fieldDefinition.name));
        }
  
        async.some(fieldDefinition.fieldOptions.definition.options, function(dropdownOption, cb) {
          //check if fieldValue and the label need to be escaped
          isSafeString(fieldValue) ? null : fieldValue = _.escape(fieldValue);
          isSafeString(dropdownOption.label) ? null : dropdownOption.label = _.escape(dropdownOption.label);
          return cb(dropdownOption.label === fieldValue);
        }, function(found) {
          if (!found) {
            return cb(new Error("Invalid option specified: " + fieldValue));
          } else {
            return cb();
          }
        });
      }
docs: validatorRadio - Validator function for radio fields.
  
  @param  {string} fieldValue        The value to validate
  @param  {object} fieldDefinition   Full JSON definition of the field
  @param  {array} previousFieldValues Any values previously stored with the fields
  @param  {function} cb               Callback function