code: public Optional<SectionHeader> maybeGetSectionHeader(
              DataDirectoryKey dataDirKey) {
          Optional<DataDirEntry> dataDir = optHeader
                  .maybeGetDataDirEntry(dataDirKey);
          if (dataDir.isPresent()) {
              return dataDir.get().maybeGetSectionTableEntry(table);
          }
          logger.warn("data dir entry " + dataDirKey + " doesn't exist");
          return Optional.absent();
      }
docs: Fetches the {@link SectionHeader} of the section the data directory entry
  for the dataDirKey points into.
  <p>
  Returns absent if the data directory doesn't exist.
  
  @param dataDirKey
  the data directory key
  @return the section table entry the data directory entry of that key
  points into or absent if there is no data dir entry for the key
  available