@Override
    public boolean isEmpty() {
        return this.bytes == null || this.bytes.length == 0;
    }
Hashes the specified byte array using the given {@code salt} for the specified number of iterations.

@param bytes          the bytes to hash
@param salt           the salt to use for the initial hash
@param hashIterations the number of times the the {@code bytes} will be hashed (for attack resiliency).
@return the hashed bytes.
@throws UnknownAlgorithmException if the {@link #getAlgorithmName() algorithmName} is not available.
crypto/hash/src/main/java/org/apache/shiro/crypto/hash/SimpleHash.java