code: function convert(value, mapping) {
      const val = mapping.converter(value);
      const validationResult = isValid(val, mapping.validator);
      if (validationResult === true) {
          return val;
      }
  
      // Make sure that we got something from the conversion.
      const message = val !== undefined && val !== null && val.toString().length > 0 ?
          `Received ${underline(JSON.stringify(value))} and it was converted to ` +
              `${underline(JSON.stringify(val))}. ` :
          '';
  
      log.warn(
          `There was a problem when trying to automatically convert ${bold(mapping.name)}. This ` +
              `value will be ignored.\n\n` +
              message + validationResult,
          'Conversion Problem'
      );
  
      return undefined;
  }
docs: /* eslint-enable