title: AssertionError when cloning Anaconda base environment
body: <p>I'm trying to create a clone of my base anaconda environment for a specific application. I want to use the clone as the base off of which to install application-specific packages. I used the following command to start the clone:</p>
  
  <pre><code>C:\Users\Liam&gt;conda create -n retrievals --clone base
  </code></pre>
  
  <p>It made it a long way through the cloning process, and had just reach 100% on cloning anaconda-5.2.0, when it threw the assertion error below:</p>
  
  <pre><code># &gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt; ERROR REPORT &lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
  
  Traceback (most recent call last):
    File "C:\Users\Liam\Anaconda3\lib\site-packages\conda\exceptions.py", line 819, in __call__
      return func(*args, **kwargs)
    File "C:\Users\Liam\Anaconda3\lib\site-packages\conda\cli\main.py", line 78, in _main
      exit_code = do_call(args, p)
    File "C:\Users\Liam\Anaconda3\lib\site-packages\conda\cli\conda_argparse.py", line 77, in do_call
      exit_code = getattr(module, func_name)(args, parser)
    File "C:\Users\Liam\Anaconda3\lib\site-packages\conda\cli\main_create.py", line 11, in execute
      install(args, parser, 'create')
    File "C:\Users\Liam\Anaconda3\lib\site-packages\conda\cli\install.py", line 211, in install
      clone(args.clone, prefix, json=context.json, quiet=context.quiet, index_args=index_args)
    File "C:\Users\Liam\Anaconda3\lib\site-packages\conda\cli\install.py", line 72, in clone
      index_args=index_args)
    File "C:\Users\Liam\Anaconda3\lib\site-packages\conda\misc.py", line 277, in clone_env
      force_extract=False, index_args=index_args)
    File "C:\Users\Liam\Anaconda3\lib\site-packages\conda\misc.py", line 78, in explicit
      assert not any(spec_pcrec[1] is None for spec_pcrec in specs_pcrecs)
  AssertionError
  </code></pre>
  
  <p><code>$ C:\Users\Liam\Anaconda3\Scripts\conda create -n retrievals --clone base</code></p>
  
  <p>Can anybody explain why this is happening and what I could try to fix it?</p>
  
  <p>P.S. I'm doing this on Windows 10 if that helps at all.</p>