code: public boolean putIfMissing(final String field, final String value) {
          return doWithJedis(new JedisCallable<Boolean>() {
              @Override
              public Boolean call(Jedis jedis) {
                  return jedis.hsetnx(getKey(), field, value) != 0;
              }
          });
      }
docs: Put <code>value</code> associated to <code>field</code>, only if field does not yet exist.
  @param field the field
  @param value the value
  @return <code>true</code> if the value was set, <code>false</code> otherwise