Update new_user_email to take id for User and perform find itself.

app/mailers/notify.rb

@@ -7,10 +7,10 @@ class Notify < ActionMailer::Base
   default from: EMAIL_OPTS["from"]
-  def new_user_email(user, password)
-    @user = user
+  def new_user_email(user_id, password)
+    @user = User.find(user_id)
     @password = password
-    mail(:to => @user['email'], :subject => "gitlab | Account was created for you")
+    mail(:to => @user.email, :subject => "gitlab | Account was created for you")
   end
   def new_issue_email(issue)

app/models/mailer_observer.rb

@@ -23,7 +23,7 @@ class MailerObserver < ActiveRecord::Observer
   end
   def new_user(user)
-    Notify.new_user_email(user, user.password).deliver
+    Notify.new_user_email(user.id, user.password).deliver
   end
   def new_note(note)

spec/mailers/notify_spec.rb

@@ -19,9 +19,9 @@ describe Notify do
   describe 'for new users, the email' do
     let(:example_site_url) { root_url }
-    let(:new_user) { Factory.new(:user, :email => 'newguy@example.com', :password => 'new_password') }
-    subject { Notify.new_user_email(new_user, new_user.password) }
+    let(:new_user) { Factory.create(:user, :email => 'newguy@example.com') }
+    subject { Notify.new_user_email(new_user.id, new_user.password) }
     it 'is sent to the new user' do
       should deliver_to new_user.email