title: TYPO3 TCA select, NULL value in items array
body: <p>I have made an extension in Typo3 4.5 with extbase and fluid. Now to insert some data i use the backend module 'list' that makes some forms with the TCA of the tables.
  To make a select box optional, I insert an item before the foreign table like this:</p>
  
  <pre><code>    'feuser' =&gt; array(
          'exclude' =&gt; 0,
          'label' =&gt; 'LLL:EXT:yes/Resources/Private/Language/locallang_db.xml:tx_yes_domain_model_schools.feuser',
          'config' =&gt; array(
              'type' =&gt; 'select',
              'items' =&gt; array(
                  array('', NULL),
              ),
              'foreign_table' =&gt; 'fe_users',
              'maxitems' =&gt; 1,
          ),
      ),
  </code></pre>
  
  <p>Now, since i have a relation (with NULL alowed) in my DB, i have to insert a NULL value. But like this it doesn't work. I have also tried '', "" and 0. But those don't work either.</p>
  
  <p>I would appreciate any help.</p>