Fix errors in DML with sublinks hidden by null expressions

src/backend/distributed/planner/multi_router_planner.c

@@ -640,7 +640,7 @@ ModifyQuerySupported(Query *queryTree, Query *originalQuery, bool multiShardQuer
 	}
 
 	/* extract range table entries */
-	ExtractRangeTableEntryWalker((Node *) queryTree, &rangeTableList);
+	ExtractRangeTableEntryWalker((Node *) originalQuery, &rangeTableList);
 
 	foreach(rangeTableCell, rangeTableList)
 	{

src/test/regress/expected/multi_modifications.out

@@ -1292,6 +1292,18 @@ HINT:  Try rewriting your queries with 'INSERT INTO ... SELECT' syntax.
 INSERT INTO summary_table (id) VALUES ((SELECT id FROM reference_summary_table));
 ERROR:  subqueries are not supported within INSERT queries
 HINT:  Try rewriting your queries with 'INSERT INTO ... SELECT' syntax.
+-- subqueries that would be eliminated by = null clauses
+DELETE FROM summary_table WHERE (
+    SELECT 1 FROM pg_catalog.pg_statio_sys_sequences
+) = null;
+DELETE FROM summary_table WHERE (
+    SELECT (select action_statement from information_schema.triggers)
+    FROM pg_catalog.pg_statio_sys_sequences
+) = null;
+ERROR:  relation pg_namespace is not distributed
+DELETE FROM summary_table WHERE id < (
+    SELECT 0 FROM pg_dist_node
+);
 DROP TABLE raw_table;
 DROP TABLE summary_table;
 DROP TABLE reference_raw_table;

src/test/regress/sql/multi_modifications.sql

@@ -867,6 +867,19 @@ INSERT INTO summary_table (id) VALUES (5), ((SELECT id FROM summary_table));
 INSERT INTO reference_summary_table (id) VALUES ((SELECT id FROM summary_table));
 INSERT INTO summary_table (id) VALUES ((SELECT id FROM reference_summary_table));
 
+-- subqueries that would be eliminated by = null clauses
+DELETE FROM summary_table WHERE (
+    SELECT 1 FROM pg_catalog.pg_statio_sys_sequences
+) = null;
+DELETE FROM summary_table WHERE (
+    SELECT (select action_statement from information_schema.triggers)
+    FROM pg_catalog.pg_statio_sys_sequences
+) = null;
+
+DELETE FROM summary_table WHERE id < (
+    SELECT 0 FROM pg_dist_node
+);
+
 DROP TABLE raw_table;
 DROP TABLE summary_table;
 DROP TABLE reference_raw_table;