query.js: do not raise if the sort_on_option list is empty

src/queries/query.js

@@ -157,6 +157,9 @@
       throw new TypeError("jioquery.sortOn(): " +
                           "Argument 1 is not of type 'array'");
     }
+    if (sort_on_option.length === 0) {
+      return list;
+    }
     list.sort(generateSortFunction(
       key_schema,
       sort_on_option

test/queries/tests.js

@@ -642,6 +642,30 @@
       });
   });*/
 
+  test('Empty sort_on options do not raise', function () {
+    var doc_list = [
+      {'a': 1},
+      {'c': 3},
+      {'b': 2}
+    ];
+
+    stop();
+    expect(1);
+    jIO.QueryFactory.create("").exec(
+      doc_list,
+      {
+        sort_on: [],
+      }
+    )
+      .then(function (list) {
+        deepEqual(list, [
+          {'a': 1},
+          {'c': 3},
+          {'b': 2}
+        ], 'Sorting didn\'t raise');
+      }).always(start);
+  });
+
   test('Multiple sort_on options', function () {
     var i,
       len = 1000,