Call to a member function diff() on null - Count days between dates [closed]

i need to create a counter between dates

Controller:

$registro = Registro::where('fechaviso', $request->id)->first();
    $fechaaviso = $registro->fechaviso;
    $fechahoy = new DateTime();
    $contadorfecha = $fechaaviso->diff($fechahoy);

I need to count the days that pass between the date of the variable: $fechaviso, to today.

error:

Call to a member function diff() on null

help pls

via Chebli Mohamed