MDL-80208 cachestore_redis: ensure empty set many with TTL don't throw.

cache/stores/redis/lib.php

@@ -447,7 +447,7 @@ class cachestore_redis extends cache_store implements cache_is_key_aware, cache_
                 $ttlparams[] = $key;
             }
         }
-        if ($usettl) {
+        if ($usettl && count($ttlparams) > 0) {
             // Store all the key values with current time.
             $this->redis->zAdd($this->hash . self::TTL_SUFFIX, [], ...$ttlparams);
             // The return value to the zAdd function never indicates whether the operation succeeded

cache/stores/redis/tests/ttl_test.php

@@ -29,7 +29,7 @@ namespace cachestore_redis;
  * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  * @covers \cachestore_redis
  */
-class ttl_test extends \advanced_testcase {
+final class ttl_test extends \advanced_testcase {
     /** @var \cachestore_redis|null Cache store  */
     protected $store = null;
 
@@ -66,6 +66,15 @@ class ttl_test extends \advanced_testcase {
         }
     }
 
+    /**
+     * Test calling set_many with an empty array
+     *
+     * Trivial test to ensure we don't trigger an ArgumentCountError when calling zAdd with invalid parameters
+     */
+    public function test_set_many_empty(): void {
+        $this->assertEquals(0, $this->store->set_many([]));
+    }
+
     /**
      * Tests expiring data.
      */