Feature: #97384 - TCA option "nullable" 

Description 

In order to further thin out the TCA eval option, the null value has been extracted into its own option: nullable, which is a boolean value.

Example:

'columns' => [
   'nullable_column' => [
       'title' => 'A nullable field',
       'config' => [
           'nullable' => true,
           'eval' => 'trim',
       ],
   ],
],

Impact 

It is now possible to define TCA fields as nullable by setting the nullable option to true. The database field should have the according NULL option set.