async function getPicture(id) {
  const user = await db.User.findByPk(id, {
    attributes: ['picture'],
  });
  if (user === null) {
    throw new NotFoundError(`User not found`);
  }
  return user.picture;
}
@private
@description This function return a user picture.
@name gladys.user.getPicture
@param {string} id - The id of the user.
@returns {Promise} Promise.
@example
await gladys.user.getPicture('6b9bc8b7-b98d-4dda-b0fd-88fc10bd0b00');