fix: closes #11343, don't crash if tags array is empty

src/database/mongo/sorted/union.js

@@ -26,7 +26,7 @@ module.exports = function (module) {
 
 	async function getSortedSetUnion(params) {
 		if (!Array.isArray(params.sets) || !params.sets.length) {
-			return;
+			return [];
 		}
 		let limit = params.stop - params.start + 1;
 		if (limit <= 0) {

src/database/postgres/sorted/union.js

@@ -32,6 +32,9 @@ SELECT COUNT(DISTINCT z."value") c
 
 	async function getSortedSetUnion(params) {
 		const { sets } = params;
+		if (!sets || !sets.length) {
+			return [];
+		}
 		const start = params.hasOwnProperty('start') ? params.start : 0;
 		const stop = params.hasOwnProperty('stop') ? params.stop : -1;
 		let weights = params.weights || [];

src/topics/tags.js

@@ -287,7 +287,7 @@ module.exports = function (Topics) {
 	}
 
 	Topics.getTagData = async function (tags) {
-		if (!tags.length) {
+		if (!tags || !tags.length) {
 			return [];
 		}
 		tags.forEach((tag) => {

test/database/sorted.js

@@ -996,6 +996,11 @@ describe('Sorted Set methods', () => {
 				done();
 			});
 		});
+
+		it('should return empty array if sets is empty', async () => {
+			const result = await db.getSortedSetRevUnion({ sets: [], start: 0, stop: -1 });
+			assert.deepStrictEqual(result, []);
+		});
 	});
 
 	describe('sortedSetIncrBy()', () => {