Handle error cases of PySequence_Length() and PySequence_GetItem().  Add an test case for zero length CA.
diff --git a/test/test_crypto.py b/test/test_crypto.py
index 684ae06..528fde4 100644
--- a/test/test_crypto.py
+++ b/test/test_crypto.py
@@ -1005,6 +1005,20 @@
         #p12 = load_pkcs12(dumped_p12, passwd)
 
 
+    def test_zero_len_list_for_ca(self):
+        """
+        Export a PKCS12 with a zero length list for CA.
+        Verify it with the openssl program.
+        """
+        passwd = 'Hobie 18'
+        p12 = self.gen_pkcs12( server_cert_pem, server_key_pem )
+        p12.set_ca_certificates( [] )
+        self.assertEqual((), p12.get_ca_certificates())
+        dumped_p12 = p12.export(passphrase=passwd, iter=3)
+        self.check_recovery(dumped_p12, key=server_key_pem, 
+                cert=server_cert_pem, passwd=passwd, )
+
+
     def test_export_without_args(self):
         """
         Run L{OpenSSL.crypto.PKCS12.export} without any