How to cast for a polymorphic pivot table?

Question

Laravel

Hello! It has 2 entities Form and Event are interconnected by a many-to-many polymorphic relationship, in the pivot table there is a pivot called values, it is stored as a json field. Is there any way to use cast for this field?
Event model code:

class Event extends Model
{
    use HasFactory;
    use HasJsonRelationships;

    protected $fillable = [
        'title'
    ];

    protected $casts = [
        'pivot.values' => 'array',
    ];

    public function forms()
    {
        return $this->morphToMany(Form::class, 'entity', 'entities_forms')
            ->withPivot('values')
            ->using(ValuesPivot::class);
    }
}

Forms model code:

class Form extends Model
{
    use HasFactory;

    protected $fillable = [
        'title',
        'structure',
    ];

    protected $casts = [
        'entity_id' => 'array',
        'structure' => 'array',
        'pivot.values' => 'array',
    ];

    

    public function events()
    {
        return $this->morphedByMany(Event::class, 'entity', 'entities_forms')->withPivot('values')->using(ValuesPivot::class);
    }
}

Values ​​Pivot code:

class ValuesPivot extends MorphPivot
{
    protected $casts = [
        'values' => 'array'
    ];
}

Result with withPivot('values'):


Result without withPivot('values'):


This problem was solved by adding the following line to the ValuePivot class:

protected $fillable = [
        'value'
    ];