Error sending form with if: else condition in laravel

I'm making a small form with the option to upload files with laravel and I ran into a problem at the time of submitting. The following problem occurs: When sending the form with upload it sends and saves normally in the bank, but without upload file it returns the error Call to a member function extension() on null . Can anyone help me?

Routes:

Route::post('/gravar', 'ManifestationController@store');  

Controller:

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use Illuminate\Support\Facades\DB;
use App\Models\Manifestation;
use App\Models\State;
use App\Http\Requests\ManifestationFormRequest;
use RealRashid\SweetAlert\Facades\Alert;

class ManifestationController extends Controller
{

private $manifestation;

public function __construct(Manifestation $manifestation)
{
    $this->manifestation = $manifestation;
}

/**
 * Display a listing of the resource.
 *
 * @return \Illuminate\Http\Response
 */
public function index()
{
    $category = DB::table('categories')->pluck('id');
    $response = ['Email', 'Telefone', 'Fax', 'Não Informado'];
    $states = DB::table('states')->pluck('letter');

    return view('site.index', [
        'category'  => $category,
        'response'  => $response,
        'states'    => $states,
        ]);
}


/**
 * Store a newly created resource in storage.
 *
 * @param  \Illuminate\Http\Request  $request
 * @return \Illuminate\Http\Response
 */
public function store(ManifestationFormRequest $request)
{
    //Nome do arquivo a ser armazenado
    $name = date('dmYHis');

    //armazena form em dataForm
    $dataForm = $request->except('_token');

    //Insere Formulário no Banco
    $insert = $this->manifestation->insert($dataForm);

    if($request->has('upload'))
    {
        //Pega extensão do arquivo original
        $extension = $request->upload->extension();
        //Armazena arquivo em Storage/app/uploads e renomeia.
        $upload = $request->upload->storeAs('uploads', $name.'.'.$extension);
    }

    Alert::success('Enviado...', 'Obrigado pela sua contribuição');
    return redirect()->route('index');
}
}

Form:

<!-- #formulario --> 
<form method="post" action="/gravar" enctype="multipart/form-data">
    {{csrf_field()}}

    <div class="form-row">
        <div class="form-group col-md-3">
            <label for="categorias">Escolha o tipo</label>
            <select id="categorias" class="form-control form-control-sm" name="FK_cat_id">
                @foreach ($category as $categories)
                    <option value="{{$categories}}">{{$categories}}</option>
                @endforeach
            </select>
        </div>
        <div class="form-group col-md-3">
            <label for="response">Receber resposta via:</label>
            <select class="form-control form-control-sm" name="response">
                @foreach ($response as $resposta)
                    <option value="{{$resposta}}">{{$resposta}}</option>
                @endforeach
            </select>
        </div>
        <div class="col-md-6 text-right">
            <input type="checkbox" name="anonimo" id="anonimo" onchange="setaCampos(this.checked)" />
            Deseja anonimato?
        </div>
    </div>

    @if (count($errors) > 0)
    <div id="ERROR_COPY" style="display: none;" class="alert alert-danger">
        <ul>
            @foreach ($errors->all() as $error)
                <li>{{$error}}</li>    
            @endforeach
        </ul>
    </div>
    @endif
    <div class="form-row">
        <div class="form-group col-md-6">
            <label for="name">Nome</label>
        <input type="text" id="name" style="text-transform:uppercase" name="name" class="form-control" placeholder="Nome completo" value="{{ old('name') }}">
        </div>
        <div class="form-group col-md-6">
            <label for="email">Email</label>
            <input type="email" name="email" class="form-control" id="email" placeholder="[email protected]" value="{{ old('email') }}">
        </div>
    </div>

    <div id="hideInf" >
        <div class="form-row">
            <div class="form-group col-md-6">
                    <label for="rg">RG</label>
                    <input type="text" name="rg" class="form-control" id="rg" value="{{ old('rg') }}">
            </div>
            <div class="form-group col-md-6">
                    <label for="cpf">CPF</label>
                    <input type="text" name="cpf" class="form-control" id="cpf" value="{{ old('cpf') }}">
            </div>
        </div>
    </div>

    <div class="form-row">
        <div class="form-group col-md-6">
            <label for="address">Endereço</label>
            <input type="text" name="address" class="form-control" id="address" placeholder="Av, Rua, QD..." value="{{ old('address') }}">
        </div>
        <div class="form-group col-md-3">
            <label for="phone">Telefone</label>
            <input type="tel" name="phone" class="form-control" id="phone_with_ddd" placeholder="(xx) ____-____" value="{{ old('phone') }}">
        </div>
        <div class="form-group col-md-3">
            <label for="fax">Fax</label>
            <input type="tel" name="fax" class="form-control" id="fax_with_ddd" placeholder="(xx) ____-____" value="{{ old('fax') }}">
        </div>
    </div>

    <div class="form-row">
        <div class="form-group col-md-6">
            <label for="city">Cidade</label>
            <input type="text" name="city" class="form-control" id="city" placeholder="Cidade em que reside" value="{{ old('city') }}">
        </div>
        <div class="form-group col-md-4">
            <label for="state">Estado</label>
            <select id="state" name="state" class="form-control" value="{{ old('state') }}">
                    @foreach ($states as $state)
                        <option selected>{{$state}}</option>
                    @endforeach
            </select>
        </div>
        <div class="form-group col-md-2">
            <label for="cep">CEP</label>
            <input type="text" name="cep" class="form-control" id="cep" value="{{ old('cep') }}">
        </div>
    </div>

    <div class="form-row col-md-6 col-xs-6">
        <div class="form-group">
            <label for="file">Enviar Arquivo</label>
            <input type="file" name="upload" class="form-control-file" value="{{ old('upload') }}">
        </div>
    </div>

    <div class="form-group">
        <label for="manifestation">Escreva Sua Mensagem</label>
        <textarea name="manifestation" class="form-control" id="manifestation" rows="12">{{ old('manifestation') }}</textarea>
    </div>

    <button type="submit" class="btn btn-success">Enviar</button>
    <button type="reset" class="btn btn-danger">Limpar</button>
</form>

error line:

  

76 $ extension = $ request-> file ('upload') -> extension ();