Hmm, why is test__core giving fits on py38/libuv/travis? Can't reproduce locally.

appveyor.yml

@@ -11,6 +11,7 @@ environment:
     # too often we get failures to resolve DNS names or failures
     # to connect on AppVeyor.
     GEVENTTEST_USE_RESOURCES: "-network"
+    PYTHONTRACEMALLOC: 10
 
   matrix:
 

src/gevent/libuv/_corecffi_source.c

@@ -157,7 +157,9 @@ static void gevent_uv_walk_callback_close(uv_handle_t* handle, void* arg)
 
 static void gevent_close_all_handles(uv_loop_t* loop)
 {
+    if (loop) {
 	uv_walk(loop, gevent_uv_walk_callback_close, NULL);
+    }
 }
 
 static void gevent_zero_timer(uv_timer_t* handle)