Correct handling of NULL arguments in json funcs.

Per gripe from Tom Lane.

Author: adunstan

src/backend/utils/adt/jsonfuncs.c

@@ -1217,8 +1217,8 @@ Datum
 json_populate_record(PG_FUNCTION_ARGS)
 {
 	Oid			argtype = get_fn_expr_argtype(fcinfo->flinfo, 0);
-	text	   *json = PG_GETARG_TEXT_P(1);
-	bool		use_json_as_text = PG_GETARG_BOOL(2);
+	text	   *json;
+	bool		use_json_as_text;
 	HTAB	   *json_hash;
 	HeapTupleHeader rec;
 	Oid			tupType;
@@ -1234,6 +1234,7 @@ json_populate_record(PG_FUNCTION_ARGS)
 	char		fname[NAMEDATALEN];
 	JsonHashEntry hashentry;
 
+	use_json_as_text = PG_ARGISNULL(2) ? false : PG_GETARG_BOOL(2);
 
 	if (!type_is_rowtype(argtype))
 		ereport(ERROR,
@@ -1267,6 +1268,8 @@ json_populate_record(PG_FUNCTION_ARGS)
 		tupTypmod = HeapTupleHeaderGetTypMod(rec);
 	}
 
+	json = PG_GETARG_TEXT_P(1);
+
 	json_hash = get_json_object_as_hash(json, "json_populate_record", use_json_as_text);
 
 	/*
@@ -1559,8 +1562,8 @@ Datum
 json_populate_recordset(PG_FUNCTION_ARGS)
 {
 	Oid			argtype = get_fn_expr_argtype(fcinfo->flinfo, 0);
-	text	   *json = PG_GETARG_TEXT_P(1);
-	bool		use_json_as_text = PG_GETARG_BOOL(2);
+	text	   *json;
+	bool		use_json_as_text;
 	ReturnSetInfo *rsi;
 	MemoryContext old_cxt;
 	Oid			tupType;
@@ -1573,6 +1576,8 @@ json_populate_recordset(PG_FUNCTION_ARGS)
 	JsonSemAction sem;
 	PopulateRecordsetState state;
 
+	use_json_as_text = PG_ARGISNULL(2) ? false : PG_GETARG_BOOL(2);
+
 	if (!type_is_rowtype(argtype))
 		ereport(ERROR,
 				(errcode(ERRCODE_DATATYPE_MISMATCH),
@@ -1616,6 +1621,8 @@ json_populate_recordset(PG_FUNCTION_ARGS)
 	if (PG_ARGISNULL(1))
 		PG_RETURN_NULL();
 
+	json = PG_GETARG_TEXT_P(1);
+
 	if (PG_ARGISNULL(0))
 		rec = NULL;
 	else