title: undefined method `reset' for RDoc::TopLevel:Class when installing a new Ruby gem
body: <p>For example,</p>
  
  <pre><code>$ gem install netaddr
  Fetching: netaddr-1.5.1.gem (100%)
  Successfully installed netaddr-1.5.1
  ERROR:  While executing gem ... (NoMethodError)
      undefined method `reset' for RDoc::TopLevel:Class
  </code></pre>
  
  <p>The NoMethodError exception keeps being raised when I install any new gem. I googled about it and searched issues in RDoc and RubyGems GitHub repositories, but had no luck.</p>
  
  <p>My Ruby version is</p>
  
  <pre><code>$ ruby -v
  ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin15]
  </code></pre>
  
  <p>The RubyGems version is</p>
  
  <pre><code>$ gem -v
  2.5.1
  </code></pre>
  
  <p>The installed RDoc version is</p>
  
  <pre><code>$ gem search rdoc -l
  
  *** LOCAL GEMS ***
  
  rdoc (4.2.2, 4.2.1)
  </code></pre>
  
  <p>I installed Ruby with RVM on Mac OS X El Capitan.</p>
  
  <p>Thanks!</p>
  
  <p><strong>[UPDATE] 2018/08/03</strong></p>
  
  <p>I haven't used my Macbook for long time, so I forgot the problem until now. The day before yesterday I got an answer notification and today I checked my situation with the same Macbook. I found that I no longer have the problem and the Ruby and Gems were updated as follows:</p>
  
  <pre><code>$ gem install netaddr
  Fetching: netaddr-2.0.3.gem (100%)
  Successfully installed netaddr-2.0.3
  Parsing documentation for netaddr-2.0.3
  Installing ri documentation for netaddr-2.0.3
  Done installing documentation for netaddr after 1 seconds
  1 gem installed
  
  $ ruby -v
  ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-darwin15]
  
  $ gem -v
  2.6.8
  
  $ gem search rdoc -l
  
  *** LOCAL GEMS ***
  
  rdoc (default: 5.0.0)
  </code></pre>
  
  <p>I don't remember when I updated them, but the problem has gone anyway, I guessed it was a bug and fixed in the updates.</p>
  
  <p>Thanks.</p>