Merge pull request #35952 from utilum/instance_var

Squash `warning: instance variable @filename not initialized`

actionview/lib/action_view/template/handlers/erb/erubi.rb

@@ -25,7 +25,7 @@ def evaluate(action_view_erb_handler_context)
             src = @src
             view = Class.new(ActionView::Base) {
               include action_view_erb_handler_context._routes.url_helpers
-              class_eval("define_method(:_template) { |local_assigns, output_buffer| #{src} }", @filename || "(erubi)", 0)
+              class_eval("define_method(:_template) { |local_assigns, output_buffer| #{src} }", defined?(@filename) ? @filename : "(erubi)", 0)
             }.empty
             view._run(:_template, nil, {}, ActionView::OutputBuffer.new)
           end