如何比较字符串null laravel

I have the following problems !

I recieve the information from the form

public function crearcomentario ()
{
    $blogId = \Request::input('identificador');  
    $autor = \Request::input('autor');  
    $correo = \Request::input('correo');  
    $content = \Request::input('content');
    $find = User::where('username','=',$autor)->get();
    $buscar = $find->toArray();
    $comentarios = new Comentario();
    //$comentarios->autor_id = $buscar[0]["id"];
    $comentarios->correo = $correo;
    $comentarios->articulo_id = $blogId;
    $comentarios->contenido = $content;
    echo $find;
    echo $autor;        
    //$comentarios->save();
}

The variable $find return the information about user introduce in the form.

My question is how can I compare if the user find is empty [] ? I try to use

if(is_null($find))

but doesn't work.

$find would be a Laravel Collection. You can use the isEmpty() function to check whether it is empty:

if($find->isEmpty()) { ... }

try this,

$find = User::where('username','=',$autor)->get();

if($find) {...}