Pass down the correct type for null parameters

src/backend/distributed/executor/multi_router_executor.c

@@ -1383,12 +1383,12 @@ ExtractParametersFromParamListInfo(ParamListInfo paramListInfo, Oid **parameterT
 		}
 
 		/*
-		 * If the parameter is NULL, or is not referenced / used (ptype == 0
+		 * If the parameter is not referenced / used (ptype == 0) and
 		 * would otherwise have errored out inside standard_planner()),
 		 * don't pass a value to the remote side, and pass text oid to prevent
 		 * undetermined data type errors on workers.
 		 */
-		if (parameterData->isnull || parameterData->ptype == 0)
+		if (parameterData->ptype == 0)
 		{
 			(*parameterValues)[parameterIndex] = NULL;
 			(*parameterTypes)[parameterIndex] = TEXTOID;
@@ -1396,8 +1396,20 @@ ExtractParametersFromParamListInfo(ParamListInfo paramListInfo, Oid **parameterT
 			continue;
 		}
 
+		/*
+		 * If the parameter is NULL then we preserve its type, but
+		 * don't need to evaluate its value.
+		 */
+		if (parameterData->isnull)
+		{
+			(*parameterValues)[parameterIndex] = NULL;
+
+			continue;
+		}
+
 		getTypeOutputInfo(parameterData->ptype, &typeOutputFunctionId,
 						  &variableLengthType);
+
 		(*parameterValues)[parameterIndex] = OidOutputFunctionCall(typeOutputFunctionId,
 																   parameterData->value);
 	}

src/test/regress/expected/multi_prepare_plsql.out

@@ -1041,6 +1041,21 @@ SELECT * FROM plpgsql_table ORDER BY key, value;
    0 |      
 (6 rows)
 
+-- check whether we can handle execute parameters
+CREATE TABLE execute_parameter_test (key int, val date);
+SELECT create_distributed_table('execute_parameter_test', 'key');
+ create_distributed_table 
+--------------------------
+ 
+(1 row)
+
+DO $$
+BEGIN
+ EXECUTE 'INSERT INTO execute_parameter_test VALUES (3, $1)' USING date '2000-01-01';
+ EXECUTE 'INSERT INTO execute_parameter_test VALUES (3, $1)' USING NULL::date;
+END;
+$$;
+DROP TABLE execute_parameter_test;
 -- clean-up functions
 DROP FUNCTION plpgsql_test_1();
 DROP FUNCTION plpgsql_test_2();

src/test/regress/sql/multi_prepare_plsql.sql

@@ -497,6 +497,17 @@ SELECT non_partition_parameter_delete(62);
 -- check table after deletes
 SELECT * FROM plpgsql_table ORDER BY key, value;
 
+-- check whether we can handle execute parameters
+CREATE TABLE execute_parameter_test (key int, val date);
+SELECT create_distributed_table('execute_parameter_test', 'key');
+DO $$
+BEGIN
+ EXECUTE 'INSERT INTO execute_parameter_test VALUES (3, $1)' USING date '2000-01-01';
+ EXECUTE 'INSERT INTO execute_parameter_test VALUES (3, $1)' USING NULL::date;
+END;
+$$;
+DROP TABLE execute_parameter_test;
+
 -- clean-up functions
 DROP FUNCTION plpgsql_test_1();
 DROP FUNCTION plpgsql_test_2();