public static byte[] add(final byte[] a, final byte[] b) {
    return add(a, b, EMPTY_BYTE_ARRAY);
  }
Concatenate byte arrays.
@param a lower half
@param b upper half
@return New array that has a in lower half and b in upper half.
hbase-common/src/main/java/org/apache/hadoop/hbase/util/Bytes.java