ErrorException Creating default object from empty value in Laravel 6

when I'm trying to update user I got this error

this error point out at $user->first_name = $request->input('first_name');

update method

 public function update($id, Request $request){
    $this->validate($request, array(
        'first_name'         => 'string|max:255',
        'last_name'         => 'string|max:255',
        'email'          => "string|email|max:255|unique:users,email,$id",
        'password'          => "sometimes|nullable |string|min:8,$id",
        'avatar'           => 'image|mimes:jpg,jpeg,gif,png,svg|max:2048',
    ));
        $password = bcrypt(request('password'));
    $user = User::where('email',$request['email'])->first();
    $user->first_name = $request->input('first_name');
    $user->last_name = $request->input('last_name');
    if(!empty($request->password))
    {
    $user->password = $password;
    }
    if($request->hasFile('avatar')){
        $avatar = $request->file('avatar');
        $filename = time() . '.' . $avatar->getClientOriginalExtension();
        Image::make($avatar)->resize(300, 300)->save( public_path('/images/avatars/' . $filename ) );
        $user->avatar = $filename;
    }
    $user->roles()->detach();
    if ($request['user']) {
        $user->roles()->attach(Role::where('name','User')->first());
    }
    if ($request['editor']) {
        $user->roles()->attach(Role::where('name','Editor')->first());
    }
    if ($request['admin']) {
        $user->roles()->attach(Role::where('name','Admin')->first());
    }
    $user->save();


    return redirect('admin/users')->with('success', 'user is successfully saved');
}

via Chebli Mohamed