can't access trees as files

lib/gollum/file.rb

@@ -47,7 +47,7 @@ module Gollum
     # Returns a Gollum::File or nil if the file could not be found.
     def find(name, version)
       if commit = @wiki.repo.commit(version)
-        if blob = commit.tree / name
+        if (blob = commit.tree / name) && blob.is_a?(Grit::Blob)
           @blob    = blob
           @path    = name
           @version = commit

test/test_file.rb

@@ -15,4 +15,8 @@ context "File" do
     assert_equal "[ ] Write section on Ents\n", file.raw_data
     assert_equal @wiki.repo.commits.first.id, file.version.id
   end
+
+  test "accessing tree" do
+    assert_nil @wiki.file("Mordor")
+  end
 end