Mis-typed input gives AttributeError: 'NoneType' object has no attribute 'groups'

[paulirwin]

If you mis-type the csr file path when executing the script, you get an unhelpful and nasty error. It should tell you that it can't find the file rather than giving this error:

paul@ubuntu:~/letsencrypt$ python sign_csr.py user.pub filethatdoesntexist.csr > signed.crt
Reading pubkey file...
Found public key!
Reading csr file...
Traceback (most recent call last):
  File "sign_csr.py", line 331, in <module>
    signed_crt = sign_csr(args.pubkey_path, args.csr_path)
  File "sign_csr.py", line 60, in sign_csr
    domain = re.search("Subject:.*? CN=([^\s,;/]+).*?", out, re.MULTILINE|re.DOTALL).groups()[0]
AttributeError: 'NoneType' object has no attribute 'groups'