Ruby : Nil salt

It is not recommended to use salt with the null value.

One of the attack methods on a password authentication system uses tables of pre-computed hash values of popular passwords. Salt is an arbitrary string, which is fed into the hash function concatenated with the original data (usually a password) in order to prevent such an attack.

Constant salt hardcoded in the application’s source code may jeopardize the security of the system. At least, the value of the salt is accessible to all the application developers. If the same salt value is used in the final version of the application, it will be possible to remove it only through an update.