title: undefined method `join' for nil:NilClass (NoMethodError) when no array is empty while using reject
body: <p>Using Ruby 1.9. I have the following:</p>
  <pre><code>add1 = [record['a'], record['b'], record['c']]
  full_add = add1.reject!(&amp;:empty?).join(&quot;, &quot;)
  
  # scenario 1
  record['a'] = 'Good'
  record['b'] = ''
  record['c'] = 'Fine'
  # &gt;&gt; Good, Fine
  
  # scenario 2
  record['a'] = 'Good'
  record['b'] = 'Boy'
  record['c'] = 'Fine'
  # &gt;&gt; undefined method `join' for nil:NilClass (NoMethodError)
  </code></pre>
  <p>When I inspect the <code>full_add</code> for scenario 2, it returns error, because no array is empty. How should I fix this? Thanks.</p>