@Override
  public boolean equals(Object o) {
    if (!(o instanceof HkdfPrfParameters)) {
      return false;
    }
    HkdfPrfParameters that = (HkdfPrfParameters) o;
    return that.getKeySizeBytes() == getKeySizeBytes()
        && that.getHashType() == getHashType()
        && Objects.equals(that.getSalt(), getSalt());
  }
Gets the salt value, which defaults to null if not set, as per RFC 5869. The HKDF PRF
implementation must convert a null salt to a string of zeros that is the length of the hash
function output.
java_src/src/main/java/com/google/crypto/tink/prf/HkdfPrfParameters.java