Downcase before save is nil is Rails - ruby-on-rails

Question

Rails 5.0.0.rc1
I want to have the username to downcase before save in rails 5.0.0.rc1 but some how username is nil:
user.rb:
before_save :downcase_username
def downcase_username
self.username.downcase!
end
Html:
<form action="/users" method="post">
<input type="text" name="user[username]" id="user_username" />
</form>
undefined method `downcase!' for nil:NilClass
I'm using React and I can create a user with a username no problem. I could have the username set to toLowerCase but I choose not to.
Why username is nil?
Edit (.jsx):
handleName: function(e){
this.setState({name: e.target.value});
}
<form action="/users" method="post">
<input type="text" name="user[username]" id="user_username"
value={this.state.name} onChange={this.handleName} placeholder="username" />
<button className="button small radius" type="submit">Register</button>
</form>
Devise controller:
def create
super do |resource|
resource.user[username] = params[:username]
resource.registration_id = params[:registration_id]
resource.save!
end
end
Logs:
Processing by Users::RegistrationsController#create as HTML
Parameters: {"user"=>{"username"=>"Test", "email"=>"test#example.com", "password"=>"[FILTERED]"}, "registration_id"=>"2"}
Unpermitted parameter: username
(0.2ms) BEGIN
User Exists (0.3ms) SELECT 1 AS one FROM "users" WHERE "users"."email" = $1 LIMIT $2 [["email", "test#example.com"], ["LIMIT", 1]]
(0.1ms) ROLLBACK
Completed 500 Internal Server Error in 159ms (ActiveRecord: 0.7ms)
Logs 2: # Data now saves but still getting downcase is nil
Started POST "/users" for ::1 at 2016-06-05 17:18:10 +0100
Processing by Users::RegistrationsController#create as HTML
Parameters: {"user"=>{"username"=>"Foo", "email"=>"foo#example.edu", "password"=>"[FILTERED]"}, "registration_id"=>"2"}
(0.1ms) BEGIN
User Exists (0.4ms) SELECT 1 AS one FROM "users" WHERE "users"."email" = $1 LIMIT $2 [["email", "foo#example.edu"], ["LIMIT", 1]]
SQL (1.1ms) INSERT INTO "users" ("email", "encrypted_password", "created_at", "updated_at", "username") VALUES ($1, $2, $3, $4, $5) RETURNING "id" [["email", "foo#example.edu"], ["encrypted_password", "$2a$11$TrrnP4391MeEMvn8e2JwMesU5JS0vGELx0.8eUVO.B4sDPZVdUFMy"], ["created_at", 2016-06-05 16:18:10 UTC], ["updated_at", 2016-06-05 16:18:10 UTC], ["username", "foo"]]
(0.9ms) COMMIT
(0.1ms) BEGIN
(0.1ms) ROLLBACK
Completed 500 Internal Server Error in 168ms (ActiveRecord: 5.5ms)

Answer 1

Update your method on user.rb to as per below:
def downcase_username
self.usernname = self.username.try(:downcase)
end

Answer 2

application_controller.rb
class ApplicationController < ActionController::Base
protected
def configure_permitted_parameters
# from new devise -v 4.1.1 gem
# devise_parameter_sanitizer.permit(:sign_up, keys: [:username])
# devise_parameter_sanitizer.permit(:account_update, keys: [:username])
#older version
devise_parameter_sanitizer.for(:sign_up) << [:username]
devise_parameter_sanitizer.for(:account_update) << [:username]
end
end