title: Difference between ?? , has_content , if_exists in freemarker
body: <p>what is the difference between the following in freemarker? </p>
  
  <pre><code>!
  has_content
  ?? 
  if_exists
  </code></pre>
  
  <p>I used ?? instead of has_content &amp; it lead to such huge issues. Screwed up my day. I really need to get this thing clarified.</p>
  
  <p>When I used </p>
  
  <pre><code>!(xyz.abc!)?? -- it dint work
  </code></pre>
  
  <p>When I used </p>
  
  <pre><code>!(xyz.abc!)?has_content ... it did work 
  </code></pre>
  
  <p>Doesn't ?? OR has_content OR if_exists check for the same thing?  </p>