strip whitespace errors from the generated Gemfile

railties/lib/rails/generators/app_base.rb

@@ -194,7 +194,7 @@ def ruby_debugger_gemfile_entry
 
       def assets_gemfile_entry
         return if options[:skip_sprockets]
-        <<-GEMFILE.strip_heredoc
+        <<-GEMFILE.strip_heredoc.gsub(/^[ \t]*$/, '')
           # Gems used only for assets and not required
           # in production environments by default.
           group :assets do

railties/test/generators/app_generator_test.rb

@@ -124,6 +124,16 @@ def test_application_names_are_not_singularized
     assert_file "hats/config/environment.rb", /Hats::Application\.initialize!/
   end
 
+  def test_gemfile_has_no_whitespace_errors
+    run_generator
+    absolute = File.expand_path("Gemfile", destination_root)
+    File.open(absolute, 'r') do |f|
+      f.each_line do |line|
+        assert_no_match /^[ \t]+$/, line
+      end
+    end
+  end
+
   def test_config_database_is_added_by_default
     run_generator
     assert_file "config/database.yml", /sqlite3/