code: @Override
    public Long setnx(final byte[] key, final byte[] value) {
      checkIsInMultiOrPipeline();
      client.setnx(key, value);
      return client.getIntegerReply();
    }
docs: SETNX works exactly like {@link #set(byte[], byte[]) SET} with the only difference that if the
  key already exists no operation is performed. SETNX actually means "SET if Not eXists".
  <p>
  Time complexity: O(1)
  @param key
  @param value
  @return Integer reply, specifically: 1 if the key was set 0 if the key was not set