[11.x] Document hashedValue as nullable

[JurianArie]

All the Hasher implementations have a null check.

framework/src/Illuminate/Hashing/Argon2IdHasher.php

Line 21 in f21afbc

if (is_null($hashedValue) || strlen($hashedValue) === 0) {

framework/src/Illuminate/Hashing/ArgonHasher.php

Line 99 in f21afbc

if (is_null($hashedValue) || strlen($hashedValue) === 0) {

framework/src/Illuminate/Hashing/BcryptHasher.php

Line 71 in f21afbc

if (is_null($hashedValue) || strlen($hashedValue) === 0) {

[taylorotwell]

I don't think you should pass null to it though.