Make sure that pg_qualstats_index_advisor always returns arrays

Thanks to github user romanstingler for the report.

CONTRIBUTORS.md

@@ -16,3 +16,4 @@
   * github user suprimex
   * github user RekGRpth
   * Zhihong Yu
+  * github user romanstingler

expected/pg_qualstats.out

@@ -149,7 +149,23 @@ FROM "PGQS".pg_qualstats() GROUP BY 1 ORDER BY 2 DESC;
  OR-ed  |     1
 (2 rows)
 
+----------------
 -- index advisor
+----------------
+-- check that empty arrays are returned rather than NULL values
+SELECT "PGQS".pg_qualstats_reset();
+ pg_qualstats_reset 
+--------------------
+
+(1 row)
+
+SELECT * FROM "PGQS".pg_qualstats_index_advisor(50);
+      pg_qualstats_index_advisor      
+--------------------------------------
+ {"indexes" : [], "unoptimised" : []}
+(1 row)
+
+-- Test some naive scenario
 CREATE TABLE adv (id1 integer, id2 integer, id3 integer, val text);
 INSERT INTO adv SELECT i, i, i, 'line ' || i from generate_series(1, 1000) i;
 SELECT "PGQS".pg_qualstats_reset();

pg_qualstats--2.0.4--2.1.0.sql

@@ -9,8 +9,8 @@ CREATE OR REPLACE FUNCTION @[email protected]_qualstats_index_advisor (
 AS $_$
 DECLARE
     v_processed bigint[] = '{}';
-    v_indexes json[];
-    v_unoptimised json[];
+    v_indexes json[] = '{}';
+    v_unoptimised json[] = '{}';
 
     rec record;
     v_nb_processed integer = 1;

pg_qualstats--2.1.0.sql

@@ -448,8 +448,8 @@ CREATE OR REPLACE FUNCTION @[email protected]_qualstats_index_advisor (
 AS $_$
 DECLARE
     v_processed bigint[] = '{}';
-    v_indexes json[];
-    v_unoptimised json[];
+    v_indexes json[] = '{}';
+    v_unoptimised json[] = '{}';
 
     rec record;
     v_nb_processed integer = 1;

test/sql/pg_qualstats.sql

@@ -43,7 +43,14 @@ SELECT COUNT(*) FROM pgqs WHERE (id = 1) OR (id > 10 AND id < 20);
 SELECT CASE WHEN qualid IS NULL THEN 'OR-ed' ELSE 'AND-ed' END kind, COUNT(*)
 FROM "PGQS".pg_qualstats() GROUP BY 1 ORDER BY 2 DESC;
 
+----------------
 -- index advisor
+----------------
+
+-- check that empty arrays are returned rather than NULL values
+SELECT "PGQS".pg_qualstats_reset();
+SELECT * FROM "PGQS".pg_qualstats_index_advisor(50);
+-- Test some naive scenario
 CREATE TABLE adv (id1 integer, id2 integer, id3 integer, val text);
 INSERT INTO adv SELECT i, i, i, 'line ' || i from generate_series(1, 1000) i;
 SELECT "PGQS".pg_qualstats_reset();