c_validator = (field, req) => {
  let i = field.charAt(0).toUpperCase() + field.substr(1)
  req.checkBody(field, `${i} is empty!!`).notEmpty()
  req.checkBody(field, `${i} must be greater than 4`).isLength({ min: 4 })
  req.checkBody(field, `${i} must be less than 32`).isLength({ max: 32 })
}
Common validators esp. in signup, edit-profile
@param {String} field
@param {Object} req