async function create(user) {
  if (!user.password || user.password.length < 8) {
    throw new BadParameters('Password is too short');
  }
  user.password = await passwordUtils.hash(user.password);
  const createdUser = await db.User.create(user);
  const plainUser = createdUser.get({ plain: true });
  delete plainUser.password;
  delete plainUser.picture;
  this.stateManager.setState('user', plainUser.selector, plainUser);
  this.stateManager.setState('userById', plainUser.id, plainUser);
  // if the instance doesn't have a clientId yet, we create it.
  const clientId = await this.variable.getValue('GLADYS_INSTANCE_CLIENT_ID');
  if (clientId === null) {
    await this.variable.setValue('GLADYS_INSTANCE_CLIENT_ID', uuid.v4());
  }
  return plainUser;
}
@public
@description This function create a user.
@name gladys.user.create
@param {object} user - A new user.
@param {string} user.firstname - The firstname of the user.
@param {string} user.lastname - The lastname of the user.
@param {string} user.email - The email of the user.
@param {string} user.password - The password for his account (min 8 characters).
@param {string} user.birthdate - The birthdate of the user.
@param {string} user.language - The language of the user.
@param {string} user.role - The role of the user (admin, habitant, guest).
@returns {Promise} Promise.
@example
await gladys.user.create({
 firstname: 'Tony'
});