code: public MerkleTreeConfig setMapName(String mapName) {
          if (StringUtil.isNullOrEmpty(mapName)) {
              throw new IllegalArgumentException("Merkle tree map name must not be empty.");
          }
          this.mapName = mapName;
          return this;
      }
docs: Sets the map name to which this config applies. Map names
  are also matched by pattern and merkle with map name "default"
  applies to all maps that do not have more specific merkle tree configs.
  
  @param mapName the map name
  @return the merkle tree config
  @throws IllegalArgumentException if the {@code mapName} is {@code null} or empty.