catch nil.to_sym errors in partial_renderer, and raise ArgumentError instead

actionpack/lib/action_view/renderer/partial_renderer.rb

@@ -407,7 +407,7 @@ module ActionView
     end
 
     def retrieve_variable(path)
-      variable = @options[:as].try(:to_sym) || path[%r'_?(\w+)(\.\w+)*$', 1].to_sym
+      variable = @options[:as].try(:to_sym) || path[%r'_?(\w+)(\.\w+)*$', 1].try(:to_sym)
       variable_counter = :"#{variable}_counter" if @collection
       [variable, variable_counter]
     end

actionpack/test/template/render_test.rb

@@ -161,6 +161,15 @@ module RenderTestCases
                                 "and is followed by any combinations of letters, numbers, or underscores.", e.message
   end
 
+  def test_render_partial_with_missing_filename
+    @view.render(:partial => "test/")
+    flunk "Render did not raise ArgumentError"
+  rescue ArgumentError => e
+    assert_equal "The partial name (test/) is not a valid Ruby identifier; " +
+                                "make sure your partial name starts with a letter or underscore, " +
+                                "and is followed by any combinations of letters, numbers, or underscores.", e.message
+  end
+
   def test_render_partial_with_incompatible_object
     @view.render(:partial => nil)
     flunk "Render did not raise ArgumentError"