test_thread_pool.rb - small JRuby fix

test_shutdown_with_grace - JRuby - rescued array may contain threads that have been GC'd, and hence are nil?

test/test_thread_pool.rb

@@ -264,6 +264,6 @@ class TestThreadPool < Minitest::Test
     end
     assert_equal 0, pool.spawned
     assert_equal 2, rescued.length
-    refute rescued.any?(&:alive?)
+    refute rescued.compact.any?(&:alive?)
   end
 end