doc for Model constructor (new) should be optional

mongoose/mongoose.d.ts

@@ -135,7 +135,7 @@ declare module "mongoose" {
   }
 
   export interface Model<T extends Document> extends NodeJS.EventEmitter {
-    new(doc: Object): T;
+    new(doc?: Object): T;
 
     aggregate(...aggregations: Object[]): Aggregate<T[]>;
     aggregate(aggregation: Object, callback: (err: any, res: T[]) => void): Promise<T[]>;