emails: fix exception when user signs up without an email.

Fix an `ActionView::Template::Error: undefined method 'verification_key'
for nil` error in the welcome_user mailer when a user signs up without
an email address.

Caused by the fact that we now render mail templates regardless of
whether the user has an email address, and then skip sending the email
only after the mail template is rendered.

app/helpers/users_helper.rb

@@ -21,6 +21,6 @@ module UsersHelper
   end
 
   def email_verification_url(user)
-    verify_user_email_url(user, email_verification_key: user.email_address.verification_key)
+    verify_user_email_url(user, email_verification_key: user.email_address&.verification_key)
   end
 end

test/unit/user_mailer_test.rb

@@ -48,6 +48,12 @@ class UserMailerTest < ActionMailer::TestCase
         mail = UserMailer.email_change_confirmation(@user)
         assert_emails(1) { mail.deliver_now }
       end
+
+      should "not fail for a user without an email address" do
+        @user = create(:user)
+        mail = UserMailer.email_change_confirmation(@user)
+        assert_emails(0) { mail.deliver_now }
+      end
     end
 
     context "welcome_user method" do
@@ -55,6 +61,12 @@ class UserMailerTest < ActionMailer::TestCase
         mail = UserMailer.welcome_user(@user)
         assert_emails(1) { mail.deliver_now }
       end
+
+      should "not fail for a user without an email address" do
+        @user = create(:user)
+        mail = UserMailer.welcome_user(@user)
+        assert_emails(0) { mail.deliver_now }
+      end
     end
   end
 end