code: private String getIntermediateMetadataFromState(WorkUnitState state, int branchId) {
      return state.getProp(
          ForkOperatorUtils.getPropertyNameForBranch(ConfigurationKeys.WRITER_METADATA_KEY, this.numBranches, branchId));
    }
docs: /*
  Retrieve intermediate metadata (eg the metadata stored by each writer) for a given state and branch id.