Adds null check for node in HasRangeTableRef (#7609)

DESCRIPTION: Adds null check for node in HasRangeTableRef to prevent
errors

src/backend/distributed/worker/worker_shard_visibility.c

@@ -504,6 +504,11 @@ FilterShardsFromPgclass(Node *node, void *context)
 static bool
 HasRangeTableRef(Node *node, int *varno)
 {
+	if (node == NULL)
+	{
+		return false;
+	}
+
 	if (IsA(node, RangeTblRef))
 	{
 		RangeTblRef *rangeTblRef = (RangeTblRef *) node;

src/test/regress/expected/system_queries.out

@@ -0,0 +1,33 @@
+-- The following query retrieves the foreign key constraints of the table "pg_dist_background_job"
+-- along with their details. This modification includes a fix for a null pointer exception that occurred
+-- in the "HasRangeTableRef" method of "worker_shard_visibility". The issue was resolved with PR #7604.
+select
+    ct.conname as constraint_name,
+    a.attname as column_name,
+    fc.relname as foreign_table_name,
+    fns.nspname as foreign_table_schema
+from
+    (SELECT ct.conname, ct.conrelid, ct.confrelid, ct.conkey, ct.contype,
+ct.confkey, generate_subscripts(ct.conkey, 1) AS s
+       FROM pg_constraint ct
+    ) AS ct
+    inner join pg_class c on c.oid=ct.conrelid
+    inner join pg_namespace ns on c.relnamespace=ns.oid
+    inner join pg_attribute a on a.attrelid=ct.conrelid and a.attnum =
+ct.conkey[ct.s]
+    left join pg_class fc on fc.oid=ct.confrelid
+    left join pg_namespace fns on fc.relnamespace=fns.oid
+    left join pg_attribute fa on fa.attrelid=ct.confrelid and fa.attnum =
+ct.confkey[ct.s]
+where
+    ct.contype='f'
+     and fc.relname='pg_dist_background_job'
+    and ns.nspname='pg_catalog'
+order by
+    fns.nspname, fc.relname, a.attnum;
+              constraint_name               | column_name |   foreign_table_name   | foreign_table_schema
+---------------------------------------------------------------------
+ pg_dist_background_task_job_id_fkey        | job_id      | pg_dist_background_job | pg_catalog
+ pg_dist_background_task_depend_job_id_fkey | job_id      | pg_dist_background_job | pg_catalog
+(2 rows)
+

src/test/regress/multi_schedule

@@ -79,7 +79,7 @@ test: multi_basic_queries cross_join multi_complex_expressions multi_subquery mu
 test: multi_subquery_complex_reference_clause multi_subquery_window_functions multi_view multi_sql_function multi_prepare_sql
 test: sql_procedure multi_function_in_join row_types materialized_view
 test: multi_subquery_in_where_reference_clause adaptive_executor propagate_set_commands geqo
-test: forcedelegation_functions
+test: forcedelegation_functions system_queries
 # this should be run alone as it gets too many clients
 test: join_pushdown
 test: multi_subquery_union multi_subquery_in_where_clause multi_subquery_misc statement_cancel_error_message

src/test/regress/sql/system_queries.sql

@@ -0,0 +1,27 @@
+-- The following query retrieves the foreign key constraints of the table "pg_dist_background_job"
+-- along with their details. This modification includes a fix for a null pointer exception that occurred
+-- in the "HasRangeTableRef" method of "worker_shard_visibility". The issue was resolved with PR #7604.
+select
+    ct.conname as constraint_name,
+    a.attname as column_name,
+    fc.relname as foreign_table_name,
+    fns.nspname as foreign_table_schema
+from
+    (SELECT ct.conname, ct.conrelid, ct.confrelid, ct.conkey, ct.contype,
+ct.confkey, generate_subscripts(ct.conkey, 1) AS s
+       FROM pg_constraint ct
+    ) AS ct
+    inner join pg_class c on c.oid=ct.conrelid
+    inner join pg_namespace ns on c.relnamespace=ns.oid
+    inner join pg_attribute a on a.attrelid=ct.conrelid and a.attnum =
+ct.conkey[ct.s]
+    left join pg_class fc on fc.oid=ct.confrelid
+    left join pg_namespace fns on fc.relnamespace=fns.oid
+    left join pg_attribute fa on fa.attrelid=ct.confrelid and fa.attnum =
+ct.confkey[ct.s]
+where
+    ct.contype='f'
+     and fc.relname='pg_dist_background_job'
+    and ns.nspname='pg_catalog'
+order by
+    fns.nspname, fc.relname, a.attnum;