title: Evaluate empty or null JSTL c tags
body: <p>How can I validate if a <code>String</code> is null or empty using the <code>c</code> tags of <code>JSTL</code>?</p>
  
  <p>I have a variable of name <code>var1</code> and I can display it, but I want to add a comparator to validate it.</p>
  
  <pre><code>&lt;c:out value="${var1}" /&gt;
  </code></pre>
  
  <p>I want to validate when it is null or empty (my values are strings).</p>