title: Unexpected '?' in LaTex reference
body: <p>Recently, I met a problem in LaTex paper writing. I want to link a website in my reference while '<b>?</b>' appeared in my context even if I have compiled the .tex file for many times.</p>
  
  <p>Here is my .bib file,</p>
  
  <pre><code>@misc{Jira,
   title = {Jira bug tracking system},
   howpublished = {\url{http://issues.apache.org/jira/}},
  }
  
  @misc{Bugzilla,
   title = {Bugzilla bug tracking system},
   howpublished = {\url{https://bz.apache.org/bugzilla/}},
  }
  </code></pre>
  
  <p>and then I refer this website in my .tex file, </p>
  
  <pre><code>\cite{Jira} 
  \cite{Bugzilla}
  </code></pre>
  
  <p>but the generated pdf looked liked this <code>[Jir(???)]</code> and <code>[Bug(???)]</code>, It's strange that other references are all showed correctly while these website references are showed '<b>?</b>'. That's the problem I really cannot figure out, who can help me and thanks a lot :)</p>