Use default from address of parent when default_from_address option is nil (#198)

Author: yenshirak

app/mailers/passwordless/mailer.rb

@@ -3,7 +3,7 @@
 module Passwordless
   # The mailer responsible for sending Passwordless' mails.
   class Mailer < Passwordless.config.parent_mailer.constantize
-    default from: Passwordless.config.default_from_address
+    default(from: Passwordless.config.default_from_address) if Passwordless.config.default_from_address
 
     # Sends a token and a magic link
     #

test/mailers/passwordless/mailer_test.rb

@@ -49,7 +49,7 @@ class Passwordless::MailerTest < ActionMailer::TestCase
       # parent class for the mailer. This means `Passwordless::Mailer` needs
       # to be reloaded, otherwise it will still have the old parent class.
       reload_mailer!
-      
+
       session = Passwordless::Session.create!(authenticatable: users(:alice), token: "hello")
       email = Passwordless::Mailer.sign_in(session, "hello")
 
@@ -60,4 +60,14 @@ class Passwordless::MailerTest < ActionMailer::TestCase
     # after the `with_config` block.
     reload_mailer!
   end
+
+  test("uses default from address of parent when default_from_address is nil") do
+    with_config({parent_mailer: "ApplicationMailer", default_from_address: nil}) do
+      reload_mailer!
+
+      assert_equal ApplicationMailer.default.fetch(:from), Passwordless::Mailer.default.fetch(:from)
+    end
+  ensure
+    reload_mailer!
+  end
 end