code: function _fixValue(v) {
      switch (typeof v) {
        case 'number':      // typeof NaN is 'number'
        case 'boolean':
        case 'undefined':
          break
        default:
          // date value returns 'new Date(NaN)' for null dates, ok
          v = v instanceof RegExp ? '' + v :
              v instanceof Date ? '(new Date(' + (+v) + '))' : // eslint-disable-line no-extra-parens
              v == null ? v : JSON.stringify(v)
          break
      }
      return v
    }
docs: ### Private methods prepare a value for inclussion in the set of variables