Fix segfault when using certain DO block in function (#7554)

When using a CASE WHEN expression in the body
of the function that is used in the DO block, a segmentation
fault occured. This fixes that.

Fixes #7381

---------

Co-authored-by: Konstantin Morozov <vzbdryn@yahoo.com>

src/backend/distributed/planner/function_call_delegation.c

@@ -91,6 +91,10 @@ bool InDelegatedFunctionCall = false;
 static bool
 contain_param_walker(Node *node, void *context)
 {
+	if (node == NULL)
+	{
+		return false;
+	}
 	if (IsA(node, Param))
 	{
 		Param *paramNode = (Param *) node;

src/test/regress/expected/function_with_case_when.out

@@ -0,0 +1,32 @@
+CREATE SCHEMA function_with_case;
+SET search_path TO function_with_case;
+-- create function
+CREATE OR REPLACE FUNCTION test_err(v1 text)
+ RETURNS text
+ LANGUAGE plpgsql
+ SECURITY DEFINER
+AS $function$
+
+begin
+  return v1 || ' - ok';
+END;
+$function$;
+do $$ declare
+ lNewValues text;
+ val text;
+begin
+ val = 'test';
+ lNewValues = test_err(v1 => case when val::text = 'test'::text then 'yes' else 'no' end);
+ raise notice 'lNewValues= %', lNewValues;
+end;$$ ;
+NOTICE:  lNewValues= yes - ok
+CONTEXT:  PL/pgSQL function inline_code_block line XX at RAISE
+-- call function
+SELECT test_err('test');
+ test_err
+---------------------------------------------------------------------
+ test - ok
+(1 row)
+
+DROP SCHEMA function_with_case CASCADE;
+NOTICE:  drop cascades to function test_err(text)

src/test/regress/multi_schedule

@@ -110,6 +110,7 @@ test: run_command_on_all_nodes
 test: background_task_queue_monitor
 test: other_databases grant_role_from_non_maindb role_operations_from_non_maindb seclabel_non_maindb
 test: citus_internal_access
+test: function_with_case_when
 
 # Causal clock test
 test: clock

src/test/regress/sql/function_with_case_when.sql

@@ -0,0 +1,27 @@
+CREATE SCHEMA function_with_case;
+SET search_path TO function_with_case;
+
+-- create function
+CREATE OR REPLACE FUNCTION test_err(v1 text)
+ RETURNS text
+ LANGUAGE plpgsql
+ SECURITY DEFINER
+AS $function$
+
+begin
+  return v1 || ' - ok';
+END;
+$function$;
+do $$ declare
+ lNewValues text;
+ val text;
+begin
+ val = 'test';
+ lNewValues = test_err(v1 => case when val::text = 'test'::text then 'yes' else 'no' end);
+ raise notice 'lNewValues= %', lNewValues;
+end;$$ ;
+
+-- call function
+SELECT test_err('test');
+
+DROP SCHEMA function_with_case CASCADE;