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

app/views/sessions/new.html.erb

@@ -1,3 +1,5 @@
+<p style="color: red"><%= notice %></p>
+
 <h1>Sign in</h1>
 
 <%= form_with url: session_path, method: :post do |form| %>