我确实按照教程中所示拉了 git repo，当我运行命令./letsencrypt-auto --apache -d example.com -d www.example.com时，example.com 是我的实际站点，它确实要求我提供联系人的电子邮件地址，但是它没有弹出剩余的操作，而是弹出此错误消息：
An unexpected error occurred:
NameError: free variable 'addrs' referenced before assignment in enclosing scope
但它创建了证书。我尝试了网站 ssllabs，但它说服务器正在侦听端口 443，但没有提供安全传输，而且https://example.com也没有实际工作（没有加载）。
我尝试再次运行它多次，甚至重新拉动 git repo，但总是出现相同的错误消息。
日志文件的完整内容（代表错误的最后 38 行，用 $USER 替换了已登录的用户）：
2016-02-11 16:59:24,530:DEBUG:letsencrypt.error_handler:Encountered exception:
Traceback (most recent call last):
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt/client.py", line 355, in deploy_certificate
fullchain_path=fullchain_path)
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt_apache/configurator.py", line 214, in deploy_cert
vhost = self.choose_vhost(domain)
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt_apache/configurator.py", line 308, in choose_vhost
vhost = self.make_vhost_ssl(vhost)
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt_apache/configurator.py", line 733, in make_vhost_ssl
self._add_name_vhost_if_necessary(ssl_vhost)
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt_apache/configurator.py", line 905, in _add_name_vhost_if_necessary
test_addr in test_vh.addrs) and
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt_apache/configurator.py", line 905, in <genexpr>
test_addr in test_vh.addrs) and
NameError: free variable 'addrs' referenced before assignment in enclosing scope
2016-02-11 16:59:24,530:DEBUG:letsencrypt.error_handler:Calling registered functions
2016-02-11 16:59:24,534:DEBUG:letsencrypt.cli:Exiting abnormally:
Traceback (most recent call last):
File "/home/$USER/.local/share/letsencrypt/bin/letsencrypt", line 11, in <module>
sys.exit(main())
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt/cli.py", line 1987, in main
return config.func(config, plugins)
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt/cli.py", line 667, in run
lineage.chain, lineage.fullchain)
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt/client.py", line 355, in deploy_certificate
fullchain_path=fullchain_path)
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt_apache/configurator.py", line 214, in deploy_cert
vhost = self.choose_vhost(domain)
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt_apache/configurator.py", line 308, in choose_vhost
vhost = self.make_vhost_ssl(vhost)
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt_apache/configurator.py", line 733, in make_vhost_ssl
self._add_name_vhost_if_necessary(ssl_vhost)
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt_apache/configurator.py", line 905, in _add_name_vhost_if_necessary
test_addr in test_vh.addrs) and
File "/home/$USER/.local/share/letsencrypt/local/lib/python2.7/site-packages/letsencrypt_apache/configurator.py", line 905, in <genexpr>
test_addr in test_vh.addrs) and
NameError: free variable 'addrs' referenced before assignment in enclosing scope
这是什么问题，我该如何解决？
感谢您的阅读。