public @Nullable RexNode getOuterJoinCond(int factIdx) {
    return multiJoin.getOuterJoinConditions().get(factIdx);
  }
Returns outer join conditions associated with the specified null-generating
factor.

@param factIdx Factor for which information will be returned
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveLoptMultiJoin.java