title: Array#split behaviour when accessing beyond the array boundry
body: <p>An <code>irb</code> session is following:</p>
  
  <pre><code>&gt;&gt; ar = [:peanute, :butter, :and, :jelly]
  =&gt; [:peanute, :butter, :and, :jelly]
  &gt;&gt; ar[0, 1]
  =&gt; [:peanute]
  &gt;&gt; ar[4, 1]
  =&gt; []
  &gt;&gt; ar[5, 1]
  =&gt; nil
  </code></pre>
  
  <p>Why ar[4, 1] does not return <code>nil</code> just like ar[5, 1]? Would someone explain this behaviour?</p>