Directly constructed `uvloop.loop.Server(None)` segfaults in `close()`

Summary

uvloop.loop.Server(None) constructs an object, but calling close() on it terminates the interpreter.
I found this while fuzzing Python C extension modules.
I realize this is not a realistic input or usage pattern, but I would expect a Python exception rather than a process crash.

Versions

uvloop 0.22.1, CPython 3.12.3, Debian 12 x86_64, glibc 2.36

Reproducer

from uvloop.loop import Server

server = Server(None)
server.close()

Segmentation fault (core dumped)

ASan/UBSan result

I built uvloop 0.22.1 from source with Clang 18 using ASan and UBSan instrumentation.
ASan reports a read from address 0x158 on the Server.close() path:

AddressSanitizer:DEADLYSIGNAL
ERROR: AddressSanitizer: SEGV on unknown address 0x000000000158
The signal is caused by a READ memory access.
Hint: address points to the zero page.

    #0 PyType_IsSubtype
    #1 CPython set operation
    #2 __Pyx_PySet_Discard  uvloop/loop.c:194862:17
    #3 Server._unref        uvloop/loop.c:160673:15
    #4 Server.close         uvloop/loop.c:161676:19

SUMMARY: AddressSanitizer: SEGV in PyType_IsSubtype

The sanitizer process exits with code 134 after ASan aborts.
UBSan did not emit a separate diagnostic before the ASan failure.

Commencez par les chemins Server.close et Server._unref identifiés dans uvloop/loop.c, puis reproduisez l’échec avec l’extrait Python utilisant Server(None). Suivez le chemin de fermeture sous ASan et vérifiez que le reproducteur lève une exception Python ou se termine autrement sans mettre fin à l’interpréteur.