Fix translate method with default: nil

    ```ruby
    I18n.translate('missing.translation', default: nil)
    # => nil
    helper.translate('missing.translation', default: nil)
    # Before
    # => "<span class=\"translation_missing\" title=\"translation missing: en.missing.translation\">Translation</span>"
    # After
    # => nil
    ```

Author: swrobel

actionview/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   `ActionView::Helpers::TranslationHelper#translate` returns nil when
+    passed `default: nil` without a translation matching `I18n#translate`.
+
+    *Stefan Wrobel*
+
 *   `OptimizedFileSystemResolver` prefers template details in order of locale,
     formats, variants, handlers.
 

actionview/lib/action_view/helpers/translation_helper.rb

@@ -58,7 +58,7 @@ module TranslationHelper
       # when you call translate in a template and translators know which keys
       # they can provide HTML values for.
       def translate(key, **options)
-        if options.has_key?(:default)
+        unless options[:default].nil?
           remaining_defaults = Array.wrap(options.delete(:default)).compact
           options[:default] = remaining_defaults unless remaining_defaults.first.kind_of?(Symbol)
         end

actionview/test/template/translation_helper_test.rb

@@ -242,6 +242,16 @@ def test_translate_with_array_of_array_default
     assert_equal [], translation
   end
 
+  def test_translate_with_false_default
+    translation = translate(:'translations.missing', default: false)
+    assert_equal false, translation
+  end
+
+  def test_translate_with_nil_default
+    translation = translate(:'translations.missing', default: nil)
+    assert_nil translation
+  end
+
   def test_translate_does_not_change_options
     options = {}
     if RUBY_VERSION >= "2.7"