PBKDF derivation compiler warning

I'm having a problem with the following usage

```
key = try PBKDF.deriveKey(fromPassword:password, salt: salt,
prf: .sha512, rounds: 1000,
derivedKeyLength: 256)
```

The compiler is telling me I have an "Ambiguous reference to member 'deriveKey(fromPassword:salt:prf:rounds:derivedKeyLength:)'

password is a String
salt is a [UInt8]
the other values are as expected

I expected the string parameter for password to enable the compiler to disambiguate the call. This is with Swift 5.0

Any thoughts? For now I'll access commoncrypto instead.