Missing import for served files

morss/wsgi.py

@@ -21,6 +21,8 @@ import re
 import lxml.etree
 
 import cgitb
+import wsgiref.util
+import mimetypes
 
 try:
     # python 2
@@ -180,7 +182,7 @@ def cgi_file_handler(environ, start_response, app):
                 # file successfully open
                 headers = {}
                 headers['status'] = '200 OK'
-                headers['content-type'] = mimetypes.guess_type(path)[0]
+                headers['content-type'] = mimetypes.guess_type(path)[0] or 'application/octet-stream'
                 start_response(headers['status'], list(headers.items()))
                 return wsgiref.util.FileWrapper(f)