Changes

node_modules/mongoose/lib/helpers/query/castUpdate.js

@@ -105,6 +105,14 @@ module.exports = function castUpdate(schema, obj, options, context, filter) {
     }
   }
 
+  if (Object.keys(ret).length === 0 &&
+      options.upsert &&
+      Object.keys(filter).length > 0) {
+    // Trick the driver into allowing empty upserts to work around
+    // https://github.com/mongodb/node-mongodb-native/pull/2490
+    return { $setOnInsert: filter };
+  }
+
   return ret;
 };