Enable testing absence of heuristic result

test/test_heuristics.rb

@@ -29,10 +29,14 @@ class TestHeuristcs < Minitest::Test
     hash.each do |language, blobs|
       Array(blobs).each do |blob|
         result = Heuristics.call(file_blob(blob), candidates)
+        if language.nil?
+          assert_equal [], result, "Failed for #{blob}"
+        else
           assert_equal [Language[language]], result, "Failed for #{blob}"
         end
       end
     end
+  end
 
   def test_detect_still_works_if_nothing_matches
     blob = Linguist::FileBlob.new(File.join(samples_path, "Objective-C/hello.m"))