next_update is not a required field on OCSP responses (#4513)

diff --git a/tests/x509/test_ocsp.py b/tests/x509/test_ocsp.py
index 0d44b6d..3ee6a26 100644
--- a/tests/x509/test_ocsp.py
+++ b/tests/x509/test_ocsp.py
@@ -319,6 +319,14 @@
         )
         assert resp.revocation_reason is x509.ReasonFlags.superseded
 
+    def test_load_revoked_no_next_update(self):
+        resp = _load_data(
+            os.path.join("x509", "ocsp", "resp-revoked-no-next-update.der"),
+            ocsp.load_der_ocsp_response,
+        )
+        assert resp.serial_number == 16160
+        assert resp.next_update is None
+
     def test_response_extensions(self):
         resp = _load_data(
             os.path.join("x509", "ocsp", "resp-revoked-reason.der"),