@Override
    public String toString() {
        return "DataFeedKey{" +
               "hash='" + hash + '\'' +
               ", salt='" + salt + '\'' +
               ", hashAlgorithmId='" + hashAlgorithm + '\'' +
               ", streamMetaData=" + streamMetaData +
               ", expiryDateEpochMs=" + expiryDateEpochMs +
               '}';
    }
Represents the hashed form of a Data Feed Key, i.e. where we only have the
hash of the key and not the key itself.
stroom-receive/stroom-receive-common/src/main/java/stroom/receive/common/HashedDataFeedKey.java