ActionController::UrlGenerationError in Users#show No route matches error - ruby-on-rails

Question

I am creating a users controller to show the users profile page but i am getting this error
ActionController::UrlGenerationError in Users#show
No route matches {:action=>"show", :controller=>"users", :id=>nil}
missing required keys: [:id] error
I am trying to add a profile page for each user so when the user for example goes to
www.mysite.com/users/jack
it will show their profile page
Here's my code:
layouts/_navbar.html.erb
<nav class="navbar navbar-default">
<div class="container-fluid">
<!-- Brand and toggle get grouped for better mobile display -->
<div class="navbar-header">
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1">
<span class="sr-only">Toggle navigation</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<a class="navbar-brand" href="/">Skillbook</a>
</div>
<!-- Collect the nav links, forms, and other content for toggling -->
<div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
<ul class="nav navbar-nav">
</ul>
<ul class="nav navbar-nav navbar-right">
<% if user_signed_in? %>
<td><%= link_to "Profile", user_path(current_user.username) %></td>
<td><%= gravatar_tag current_user.email, size: 20 %><%= current_user.username %></td>
<li><%= link_to "Edit user", edit_user_registration_path %></li>
<li><%= link_to "Log out", destroy_user_session_path ,method: :delete %></li>
<%else%>
<li><%= link_to "Log in", new_user_session_path %></li>
<li><%= link_to " Sign up", new_user_registration_path%></li>
<%end%>
</ul>
</ul>
</div><!-- /.navbar-collapse -->
</div><!-- /.container-fluid -->
</nav>
users_controller.rb
class UsersController < ApplicationController
before_action :set_user, only: [:show]
private
def set_user
#user = User.find_by(username: params[:id])
end
end
routes.rb
Rails.application.routes.draw do
get 'pages/home'
devise_for :users
root 'pages#home'
resources :users, only: [:show, :index]
end

Answer 1

Well, this error simply is what it is:
missing required keys: [:id]
Where, according to your setup, is the username of the currently signed-in user.
In a nutshell, what this is telling you is that you are trying to pass in the username of the signed-in user, but for this instance, the user that is signed in has no username.
To fix this, make sure that the username of the signed-in user, (and all other users for that matter) is not nil

Answer 2

In url you should pass an id of the user, and you do not do that.
What you really want to incorporate is friendly_id gem.
With it set up you will be able to actually present users id as name(or whatever other attribute/combination of attributes you want):
www.mysite.com/users/1
will become
www.mysite.com/users/jack

Answer 3

In your routes file add
get '/users/:id', to: 'users#show', as: '/users/:username'
The last part as: is where you are naming your route. This would give the user with username 'jack' the route /users/jack. Likewise if you wanted to get rid of users altogether you could put as: '/:username'
No need to install another gem.
Justin