docs: private static void simplifyOuterJoin(BranchNode joinTree) {
          assert(joinTree != null);
          List<AbstractExpression> exprs = new ArrayList<>();
          JoinNode leftNode = joinTree.getLeftNode();
          JoinNode rightNode = joinTree.getRightNode();
          // For the top level node only,
          // WHERE expressions need to be evaluated for NULL-rejection
          if (leftNode.getWhereExpression() != null) {
              exprs.add(leftNode.getWhereExpression());
          }
          if (rightNode.getWhereExpression() != null) {
              exprs.add(rightNode.getWhereExpression());
          }
          simplifyOuterJoinRecursively(joinTree, exprs);
      }