concat should ignore nil

actionpack/lib/action_view/helpers/text_helper.rb

@@ -26,7 +26,7 @@ module TextHelper
       #       # will either display "Logged in!" or a login link
       #   %>
       def concat(string)
-        if @output_buffer
+        if @output_buffer && string
           @output_buffer << string
         else
           string

actionpack/test/template/text_helper_test.rb

@@ -11,6 +11,14 @@ def setup
     @_cycles = nil if (defined? @_cycles)
   end
 
+  def test_concat
+    @output_buffer = 'foo'
+    concat 'bar'
+    assert_equal 'foobar', @output_buffer
+    assert_nothing_raised { concat nil }
+    assert_equal 'foobar', @output_buffer
+  end
+
   def test_simple_format
     assert_equal "<p></p>", simple_format(nil)