public function addUser(Request $request){
        $user = new User();
        $user->firstName = $request->firstName;
        $user->lastName = $request->lastName;
        $user->login = $request->login;
        $user->password = bcrypt($request->password);
        if(empty($request->image)){

            $user->image = NULL;

           } else{
                $custom_file_name = $request->image->getClientOriginalName();
                $path = $request->image->storeAs('avatars',$custom_file_name);
                $user->image = $path;
            }
        $user->save();
        return response()->json($user);
    }

$(document).on('click', "#add", function() {

            var firstName = $('#firstName').val();
            var lastName = $('#lastName').val();
            var login = $('#login').val();
            var password = $('#password').val();
            var image  = $('#image').prop('files')[0];

            var form_data = new FormData();

            form_data.append('firstName', firstName);
            form_data.append('lastName', lastName);
            form_data.append('login', login);
            form_data.append('password', password);
            form_data.append('image', image);

                    $.ajax({
                      url: "{{action('UserController@addUser')}}",
                      method: 'POST',
                      data:form_data,
                      contentType: false,
                      processData: false,
                      success: function(data) {


                        toastr.success('', 'Success!');
                      },

                      error: function(){
                          toastr.error('', 'Error!');
                      }
                    });

<form enctype="multipart/form-data">
 {{ csrf_field() }}
   <div class="form-group">
    <input type="text" id="lastName" autocomplete="off" class="form-control" />
   </div>
   <div class="form-group">
    <input type="text" id="firstName" autocomplete="off" class="form-control" />
   </div>
   <div class="form-group">
    <input type="text" id="login" autocomplete="off" class="form-control" />
   </div>
   <div class="form-group">
    <input type="password" id="password" autocomplete="off" class="form-control" />
   </div>
   <div class="form-group">
    <input type="file" id="image" name="image" autocomplete="off" class="form-control" />
   </div>
</form>
<button type="submit" id="add" class="btn default">Add</button>

$table->string('email')->nullable();

$table->string('image')->nullable();