public static byte[] head(final byte[] a, final int length) {
        if (a.length < length) {
            return null;
        }
        byte[] result = new byte[length];
        System.arraycopy(a, 0, result, 0, length);
        return result;
    }
Make a new byte array from a subset of bytes at the head of another.

@param a      array
@param length amount of bytes to grab
@return First <code>length</code> bytes from <code>a</code>
stroom-bytebuffer/src/main/java/stroom/bytebuffer/hbase/Bytes.java