restore ability to reset the session

types/koa-session/index.d.ts

@@ -213,7 +213,7 @@ declare function session(app: Koa): Koa.Middleware;
 
 declare module "koa" {
     interface Context {
-        session: session.Session | undefined;
+        session: session.Session | null;
         readonly sessionOptions: session.opts | undefined;
     }
 

types/koa-session/koa-session-tests.ts

@@ -39,4 +39,11 @@ app.use(session({
     },
 }, app));
 
+app.use((ctx, next) => {
+    // reset the session
+    ctx.session = null;
+
+    return next();
+})
+
 app.listen(3000);