Handle empty arrays passed to collections

[cviebrock]

I was running into issues in my Laravel project using laravel-fractal with this code:

$items = [];
$fractal = fractal($items, $transformer, new ArraySerializer);

I traced it back to this line in fractalistic:

// src/Fractal.php

    public static function create($data = null, $transformer = null, $serializer = null)
    {
        $instance = new static(new Manager());

        $instance->data = $data ?: null;    // <--- HERE
        $instance->dataType = $instance->determineDataType($data);
        $instance->transformer = $transformer ?: null;
        $instance->serializer = $serializer ?: null;

        return $instance;
    }

If for whatever reason you end up passing an empty array as data, the ternary operator treats it as false, and $instance->data is set to null. Then $instance->dataType is set "collection" (since an array is passed to it). Eventually, this throws an exception:

Invalid argument supplied for foreach() /home/admin/domains/www.wareable.local/vendor/league/fractal/src/Scope.php
line 317

because it is trying to foreach over null (i.e. not an array).

This PR (plus accompanying test) fixes it but not trying to do any transformation on the data that gets passed to Fractal::create().

[freekmurze]

Perfect little PR, thanks!