fix: don't crash if tid is falsy

src/topics/posts.js

@@ -22,7 +22,10 @@ module.exports = function (Topics) {
 	};
 
 	Topics.getTopicPosts = async function (topicOrTid, set, start, stop, uid, reverse) {
-		if (topicOrTid && typeof topicOrTid !== 'object') {
+		if (!topicOrTid) {
+			return [];
+		}
+		if (typeof topicOrTid !== 'object') {
 			// TODO: remove in 1.19.0
 			winston.warn('[deprecated] Topics.getTopicPosts(tid, ...) usage is deprecated, pass a topic object as first argument!');
 			topicOrTid = await Topics.getTopicData(topicOrTid);

test/topics.js

@@ -502,6 +502,11 @@ describe('Topic\'s', () => {
 					assert.strictEqual(post.index, index);
 				});
 			});
+
+			it('should return empty array if first param is falsy', async () => {
+				const posts = await topics.getTopicPosts(null, `tid:${tid}:posts`, 0, 9, topic.userId, true);
+				assert.deepStrictEqual(posts, []);
+			});
 		});
 	});