Handle null values using a Juicer

[rgazelot]

Hi there, it's me again!

I found a weird case to handle : I wanted to use a Juicer on a field and when I wrote tests I tried with a null value and found that it throws a php exception about the clean process.

$validator
  ->addField('foo', true)
    ->addJuicer('foo', (new \Chanmix51\ParameterJuicer\ParameterJuicer)
        ->addField('bar', true)
          ->addValidator('bar', function($v) {
            if ("baz" !== $v) {
              throw new \Chanmix51\ParameterJuicer\ValidationException('error.');
            }
          })
    )
;

$data = [
  'foo' => null,
];

$data = $validator->squash($data);

// PHP Fatal error:  Uncaught TypeError: Argument 1 passed to Chanmix51\ParameterJuicer\ParameterJuicer::clean() must be of the type array, null given in /vendor/chanmix51/parameter-juicer/sources/lib/ParameterJuicer.php:348

I think that this case should be handle, what do you think?