docs: private BranchTuples getBranchTuples(LeftTupleSink sink, LeftTuple leftTuple) {
          BranchTuples branchTuples = new BranchTuples();
          LeftTuple child = leftTuple.getFirstChild();
          if ( child != null ) {
              // assigns the correct main or rtn LeftTuple based on the identified sink
              if ( child.getTupleSink() == sink ) {
                  branchTuples.mainLeftTuple = child;
              } else {
                  branchTuples.rtnLeftTuple = child;
              }
              child = child.getHandleNext();
              if ( child != null ) {
                  if ( child.getTupleSink() == sink ) {
                      branchTuples.mainLeftTuple = child;
                  } else {
                      branchTuples.rtnLeftTuple = child;
                  }
              }
          }
          return branchTuples;
      }