Fix multi.exec with empty queue and previous watch

When calling exec on a multi instance which you did not use, no command is sent currently.

This is a problem for watched keys, because no EXEC means no unwatch, which might cause hard-to-debug problems.

Proposed Fix: Sending UNWATCH

Author: Mik13

packages/client/lib/client/multi-command.ts

@@ -171,7 +171,6 @@ export default class RedisClientMultiCommand {
         }
 
         const commands = this.#multi.exec();
-        if (!commands) return [];
 
         return this.#multi.handleExecReplies(
             await this.#executor(

packages/client/lib/cluster/multi-command.ts

@@ -121,7 +121,6 @@ export default class RedisClusterMultiCommand {
         }
 
         const commands = this.#multi.exec();
-        if (!commands) return [];
 
         return this.#multi.handleExecReplies(
             await this.#executor(commands, this.#firstKey, RedisMultiCommand.generateChainId())

packages/client/lib/multi-command.spec.ts

@@ -46,14 +46,16 @@ describe('Multi Command', () => {
     });
 
     describe('exec', () => {
-        it('undefined', () => {
+        it('without commands', () => {
             assert.equal(
                 new RedisMultiCommand().exec(),
-                undefined
+                [
+                  { args: ['UNWATCH'] }
+                ]
             );
         });
 
-        it('Array', () => {
+        it('with commands', () => {
             const multi = new RedisMultiCommand();
             multi.addCommand(['PING']);
 

packages/client/lib/multi-command.ts

@@ -69,9 +69,9 @@ export default class RedisMultiCommand {
         return transformedArguments;
     }
 
-    exec(): undefined | Array<RedisMultiQueuedCommand> {
+    exec(): Array<RedisMultiQueuedCommand> {
         if (!this.queue.length) {
-            return;
+            return [{ args: ['UNWATCH'] }];
         }
 
         return [