Fix NULL input behaviour of pg_stat_get_replication_slot().

pg_stat_get_replication_slot() accidentally was marked as non-strict, crashing
when called with NULL input. As it's already released, introduce an explicit
NULL check in 14, fix the catalog in HEAD.

Bumps catversion in HEAD.

Discussion: https://postgr.es/m/20220326212432.s5n2maw6kugnpyxw@alap3.anarazel.de
Backpatch: 14-, where replication slot stats were introduced

src/backend/utils/adt/pgstatfuncs.c

@@ -2315,7 +2315,7 @@ Datum
 pg_stat_get_replication_slot(PG_FUNCTION_ARGS)
 {
 #define PG_STAT_GET_REPLICATION_SLOT_COLS 10
-	text	   *slotname_text = PG_GETARG_TEXT_P(0);
+	text	   *slotname_text;
 	NameData	slotname;
 	TupleDesc	tupdesc;
 	Datum		values[PG_STAT_GET_REPLICATION_SLOT_COLS];
@@ -2323,6 +2323,15 @@ pg_stat_get_replication_slot(PG_FUNCTION_ARGS)
 	PgStat_StatReplSlotEntry *slotent;
 	PgStat_StatReplSlotEntry allzero;
 
+	/*
+	 * Function was accidentally marked as non-strict, can't change that post
+	 * release.
+	 */
+	if (PG_ARGISNULL(0))
+		PG_RETURN_NULL();
+
+	slotname_text = PG_GETARG_TEXT_P(0);
+
 	/* Initialise values and NULL flags arrays */
 	MemSet(values, 0, sizeof(values));
 	MemSet(nulls, 0, sizeof(nulls));

src/test/regress/expected/stats.out

@@ -201,4 +201,11 @@ FROM prevstats AS pr;
 
 DROP TABLE trunc_stats_test, trunc_stats_test1, trunc_stats_test2, trunc_stats_test3, trunc_stats_test4;
 DROP TABLE prevstats;
+-- ensure that stats accessors handle NULL input correctly
+SELECT pg_stat_get_replication_slot(NULL);
+ pg_stat_get_replication_slot 
+------------------------------
+ 
+(1 row)
+
 -- End of Stats Test

src/test/regress/sql/stats.sql

@@ -176,4 +176,10 @@ FROM prevstats AS pr;
 
 DROP TABLE trunc_stats_test, trunc_stats_test1, trunc_stats_test2, trunc_stats_test3, trunc_stats_test4;
 DROP TABLE prevstats;
+
+
+-- ensure that stats accessors handle NULL input correctly
+SELECT pg_stat_get_replication_slot(NULL);
+
+
 -- End of Stats Test