PHP filter callback with default value - php

Question

Is there a way to define a default value (or to force the callback to be called everytime) when using filter_var_array and FILTER_CALLBACK ?
Example data:
{
"name": "John"
}
Example usage:
$params = filter_var_array($datas_from_above, [
'name' => FILTER_SANITIZE_STRING,
'age' => [
'filter' => FILTER_CALLBACK,
'options' => function ($data) {
// I was thinking $data would be null here
// but this function is not called if the
// param is not present in the input array.
die('stop?');
}
]
], true); // Add missing keys as NULL to the return value
When using other filters, there's the default option. So it shouldn't be supernatural to have a default value for callback filters. Am I missing something obvious?
Thanks

Answer 1

ok so after some comments and digging, filters in php only process what the input array contains.
So if you want to guarantee that a custom callback is always called, even if the input array doesn't contain the key => value pair, you can do:
$partial_input = ["name" => "John"]; // E.g. from a GET request
$defaults = ["name" => null, "age" => null];
$input = array_merge($defaults, $partial_input);
$parsed = filter_var_array($input, [
"name" => FILTER_SANITIZE_STRING,
"age" => [
"filter" => FILTER_CALLBACK,
"options" => function ($data) {
// do something special if $data === null
}
]
]);