title: fetch() returns : warning: block supersedes default value argument
body: <p>Why do I get this warning and what it means?</p>
  
  <pre><code>a = [1,3,5]
  a.fetch(0) #=&gt; 1
  a.fetch(0,0) #=&gt; 1
  
  a.fetch(22) { "out of range" } #=&gt; out of range
  a.fetch(0,0) { "out of range" } #=&gt; returns 1 with warning: block supersedes default value argument
  </code></pre>