Null values in FactoryMuffin define - php

Question

I am using PhPUnit, FactoryMuffin and Faker for testing in Laravel, with a PostgreSQL db. In the previous version of FactoryMuffin (Zizaco\FactoryMuff) I could assign null values to columns both in the static factory array and when calling FactoryMuff::create.
However this no longer works - if I use the following define:
FactoryMuffin::define('MyModel', array(
'name' => 'word',
'empty' => null,
'another' => 'word'
));
when I call FactoryMuffin::create instead of passing NULL to the SQL INSERT statement it leaves the value blank, so I get:
INSERT INTO my_table ("name", "empty", "another") VALUES ('Ralph', , 'Someone');
which PGSQL doesn't allow. The same thing happens using
FactoryMuffin::create('MyModel', array('empty' => null));
Any ideas how to get round this, beyond instantiating the model and then assigning null to the field?

Answer 1

Since FactoryMuffin 2.1 (and 3.*) you can take advantage of the callback functionality, e.g.:
FactoryMuffin::define('MyModel', array(
'name' => 'word',
'empty' => null,
'another' => 'word'
))->setCallback(function ($object, $saved) {
$object->empty = null;
});
In FactoryMuffin 2.1 the callback is set as the third parameter of the define:
FactoryMuffin::define('MyModel', array(
'name' => 'word',
'empty' => null,
'another' => 'word'
), function ($object, $saved) {
$object->empty = null;
});