Do we need uniqueness index for encrypted_otp_secret_key?

[airled]

The gem automatically creates migration file with this index:

...
add_index :users, :encrypted_otp_secret_key, unique: true
...

It's not a big deal really. Just can't undestand why do we need it? Even if you create several users with same otp_secret_key, the salt and iv most likely be different for both of the users. So encrypted_otp_secret_key field will be different too. Seems like the index is pretty pointless. What do you think?