incorrect login redirects back to sign-in

app/controllers/sessions_controller.rb

@@ -4,8 +4,12 @@ class SessionsController < ApplicationController
 
   def create
     user = User.find_by username: params[:username]
-    session[:user_id] = user.id if user
-    redirect_to user
+    if user.nil?
+      redirect_to signin_path, notice: "User #{params[:username]} does not exist!"
+    else
+      session[:user_id] = user.id if user
+      redirect_to user
+    end
   end
 
   def destroy