code: public ReadModifyWriteRow increment(
        @Nonnull String familyName, @Nonnull String qualifier, long amount) {
      return increment(familyName, ByteString.copyFromUtf8(qualifier), amount);
    }
docs: Adds `amount` be added to the existing value. If the targeted cell is unset, it will be treated
  as containing a zero. Otherwise, the targeted cell must contain an 8-byte value (interpreted as
  a 64-bit big-endian signed integer), or the entire request will fail.