Unhandled exception (#e5c0582b)

[sqlmapreporter]

sqlmap version: 1.0-dev-nongit-20141123
Python version: 2.7.5
Operating system: nt
Command line: sqlmap.py -u ************************************************** --os-shell
Technique: UNION
Back-end DBMS: MySQL (fingerprinted)

Traceback (most recent call last):
  File "sqlmap.py", line 100, in main
    start()
  File "lib/controller/controller.py", line 596, in start
    action()
  File "lib/controller/action.py", line 160, in action
    conf.dbmsHandler.osShell()
  File "plugins/generic/takeover.py", line 80, in osShell
    self.initEnv(web=web)
  File "lib/takeover/abstraction.py", line 183, in initEnv
    self.webInit()
  File "lib/takeover/web.py", line 323, in webInit
    if not self.webUpload(backdoorName, posixToNtSlashes(directory) if Backend.isOs(OS.WINDOWS) else directory, content=backdoorContent):
  File "lib/takeover/web.py", line 98, in webUpload
    return self._webFileStreamUpload(stream, destFileName, directory)
  File "lib/takeover/web.py", line 119, in _webFileStreamUpload
    page = Request.getPage(url=self.webStagerUrl, multipart=multipartParams, raise404=False)
  File "lib/request/connect.py", line 284, in getPage
    conn = multipartOpener.open(unicodeencode(url), multipart)
  File "Python27/lib/urllib2.py", line 402, in open
    req = meth(req)
  File "thirdparty/multipart/multipartpost.py", line 67, in http_request
    boundary, data = self.multipart_encode(v_vars, v_files)
  File "thirdparty/multipart/multipartpost.py", line 86, in multipart_encode
    buf += '\r\n\r\n' + value + '\r\n'
TypeError: cannot concatenate 'str' and 'NoneType' objects