title: Check if value isset and null
body: <p>I need to check if value is defined as anything, including null. <code>isset</code> treats null values as undefined and returns <code>false</code>. Take the following as an example:</p>
  
  <pre><code>$foo = null;
  
  if(isset($foo)) // returns false
  if(isset($bar)) // returns false
  if(isset($foo) || is_null($foo)) // returns true
  if(isset($bar) || is_null($bar)) // returns true, raises a notice
  </code></pre>
  
  <p>Note that <code>$bar</code> is undefined.</p>
  
  <p>I need to find a condition that satisfies the following:</p>
  
  <pre><code>if(something($bar)) // returns false;
  if(something($foo)) // returns true;
  </code></pre>
  
  <p>Any ideas?</p>