code: public static String getPropertyNameForBranch(WorkUnitState workUnitState, String key) {
      Preconditions.checkNotNull(workUnitState, "Cannot get a property from a null WorkUnit");
      Preconditions.checkNotNull(key, "Cannot get a the value for a null key");
  
      if (!workUnitState.contains(ConfigurationKeys.FORK_BRANCH_ID_KEY)) {
        return key;
      }
      return workUnitState.getPropAsInt(ConfigurationKeys.FORK_BRANCH_ID_KEY) >= 0
          ? key + "." + workUnitState.getPropAsInt(ConfigurationKeys.FORK_BRANCH_ID_KEY) : key;
    }
docs: Get a new property key from an original one based on the branch id. The method assumes the branch id specified by
  the {@link ConfigurationKeys#FORK_BRANCH_ID_KEY} parameter in the given WorkUnitState. The fork id key specifies
  which fork this parameter belongs to. Note this method will only provide the aforementioned functionality for
  {@link org.apache.gobblin.converter.Converter}s. To get the same functionality in {@link org.apache.gobblin.writer.DataWriter}s use
  the {@link org.apache.gobblin.writer.DataWriterBuilder#forBranch(int)} to construct a writer with a specific branch id.
  
  @param workUnitState contains the fork id key
  @param key           property key
  @return a new property key