code: protected <T> Map<String, CompletableFuture<T>> executeOnMasters(
              Function<RedisClusterAsyncCommands<K, V>, RedisFuture<T>> function) {
          return executeOnNodes(function, redisClusterNode -> redisClusterNode.is(MASTER));
      }
docs: Run a command on all available masters,
  
  @param function function producing the command
  @param <T> result type
  @return map of a key (counter) and commands.