Call to a member function store() on null on Laravel Livewire image upload

I have the following functionality that was working correctly but suddenly it stopped working and I can't detect what the problem is.

It doesn't have a form and I don't use the request either. That's why I run it from Livewire:

Blade

<div class="form-group">
       <label for="portada">Portada <small class="text-danger">*</small></label>
       <input wire:model="portada" type="file" class="form-control-file" name="portada" id="portada">
</div>

Component

//Guardamos la foto de portada
    $pathFoto = $this->foto->store('imagenPortada');



    // Creamos primero el usuario
    User::create([
            'tipo_usuario' => $this->tipo_de_usuario,
            'name' => $this->nombre_usuario,
            'apellido' => $this->apellido_usuario,
            'documento' => $this->documento_usuario,
            'telefono' => $this->telefono_usuario,
            'telegram' => $this->telegram,
            'email' => $this->email,
            'password' => Hash::make($this->password),
            'permiso' => $this->permiso,
            'perfil' => asset($pathFoto)
        ]);

The error:

Call to a member function store() on null {"exception":"[object] (Error(code: 0): Call to a member function store() on null

Solution: Thanks @L.Flor, do it as follows:

public $foto = null;


if(!empty($this->foto)){
        $pathFoto = $this->foto->store('imagenPortada');
    }else{
        $pathFoto = null;
    }