Backend TCA: possible to make a field nullable? - typo3

Question

I need a backend field where users can enter a time (ie "23:13:46", hours, minutes, seconds). But it should also be possible to not enter a time at all (which should of course be different from 00:00:00). Is it possible to make a field nullable?
What I have so far is this:
$GLOBALS['TCA']['tx_something_domain_model_delivery'] = array(
'columns' => array(
'deadline' => array(
'exclude' => 1,
'label' => 'Deadline',
'config' => array(
'dbType' => 'time',
'type' => 'input',
),
),
...
),
);
But if I enter nothing in the Deadline field, it stores "00:00:00" to the database. The database looks like this:
CREATE TABLE IF NOT EXISTS `tx_something_domain_model_delivery` (
`uid` int(11) NOT NULL,
`pid` int(11) NOT NULL DEFAULT '0',
`deadline` time DEFAULT NULL,
...
);
so deadline is nullable, but I don't know how to achieve this.
BTW: I'm a newbie at typo3, so if you think the way I create the field is retarded or there is a much better way, I'd be thankful for any suggestions.

Answer 1

First: You are creating the field exactly in the intended way :-)
Second: You need to use the eval property in the configuration of the field. Add the setting null to it. Your config should then look like this:
$GLOBALS['TCA']['tx_something_domain_model_delivery'] = array(
'columns' => array(
'deadline' => array(
'exclude' => 1,
'label' => 'Deadline',
'config' => array(
'dbType' => 'time',
'type' => 'input',
'eval' => 'null',
),
),
...
),
);
There are more settings for the eval setting that might be of interest to you.