Don't crash on listen unix: (#4259)

Fixes #4225.

* don't crash on listen unix:

* correctly merge #4221

certbot-nginx/certbot_nginx/parser.py

@@ -586,9 +586,10 @@ def _parse_server_raw(server):
             continue
         if directive[0] == 'listen':
             addr = obj.Addr.fromstring(directive[1])
-            parsed_server['addrs'].add(addr)
-            if addr.ssl:
-                parsed_server['ssl'] = True
+            if addr:
+                parsed_server['addrs'].add(addr)
+                if addr.ssl:
+                    parsed_server['ssl'] = True
         elif directive[0] == 'server_name':
             parsed_server['names'].update(
                 _get_servernames(directive[1]))

certbot-nginx/certbot_nginx/tests/parser_test.py

@@ -323,6 +323,12 @@ class NginxParserTest(util.NginxTest):
         ])
         self.assertTrue(server['ssl'])
 
+    def test_parse_server_raw_unix(self):
+        server = parser._parse_server_raw([ #pylint: disable=protected-access
+            ['listen', 'unix:/var/run/nginx.sock']
+        ])
+        self.assertEqual(len(server['addrs']), 0)
+
     def test_parse_server_global_ssl_applied(self):
         nparser = parser.NginxParser(self.config_path, self.ssl_options)
         server = nparser.parse_server([