[FLOW3-general] form validation

[Winfried Holler]

I need some help with form validation .
In my form there is a textfield (days) for an integer value.
If  the textfield is empty I get this exception when submitting the form 
(newAction):

Integrity constraint violation: 1048 Column 'days' cannot be null

How can I avoid this exception?  Where can I define a default value, if days 
is null?

definition in model:
 /**
  * The days
  * @var integer
   * @FLOW3\Validate(type="NotEmpty")
   * @FLOW3\Validate(type="Integer", options={ "minimum"=1, "maximum"=100 })
  */
 protected $days

thx