表单提交验证不通过

问题

表单提交到验证类时报错。
如果同时提交字符串类型和数组就报错。单提交字符串或数组就不报错。
问题出在哪里？

表单

    <form id="fleets" method="post" action="@if($fleet->id > 0) /fleets/ {{$fleet->id}} @else /fleets @endif">
                @csrf
                <input type="text" name="fleet_name">
                <br>
                <input type="text" name="car[]">
                <input type="text" name="car[]">
                <input type="text" name="car[]">
            </form>

验证类

    use Illuminate\Foundation\Http\FormRequest;
use Illuminate\Validation\Rule;

class FleetRequest extends FormRequest
{
    /**
     * Determine if the user is authorized to make this request.
     *
     * @return bool
     */
    public function authorize()
    {
        return true;
    }

    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules()
    {
        return [
            'fleet_name' => ['required'],
            'car.' => ['required'],
        ];
    }
}