Couldn't find User with 'id'=search omniauth facebook

I am working on a web on rails and have been having issues logging into facebook. The error I get is

Couldn't find User with 'id'=2

My index.html.erb (where the login in happening), the relevant code is as follows:

 <% if current_user %>
  Signed in as <strong><%= current_user.name %></strong>!
  <%= link_to "Sign out", signout_path, id: "sign_out" %>
 <% else %>
<% end %>

In my application controller I have:

 def current_user
 @current_user ||= User.find(session[:user_id]) if session[:user_id]
 end

I referred to this question but I just get redirected to the homepage (index) without actually being logged in. What is going wrong here?