Merge branch 'master' into develop

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 || [];