empty array if not topics in catgory

src/categories.js

@@ -93,7 +93,13 @@ var db = require('./database'),
 				topics.getTopicsByTids(tids, cid, uid, next);
 			},
 			function(topics, next) {
-				if (topics && topics.length > 0) {
+				if (!topics || !topics.length) {
+					return next(null, {
+						topics: [],
+						nextStart: 1
+					});
+				}
+
 				db.sortedSetRevRank('categories:' + cid + ':tid', topics[topics.length - 1].tid, function(err, rank) {
 					if(err) {
 						return next(err);
@@ -104,12 +110,6 @@ var db = require('./database'),
 						nextStart: parseInt(rank, 10) + 1
 					});
 				});
-				} else {
-					next(null, {
-						topics: topics,
-						nextStart: 1
-					});
-				}
 			}
 		], callback);
 	};