От чего ошибка «Trying to get property of non-object»?

$test = Tests::where('category_id','=',$category_id)->first();
		dd($test);

$test = Tests::where('category_id', intval($category_id))->first();

public function getTest($category_id){
		$category_id2 = 36;
		If ($category_id==$category_id2) {
			dd('равны');
		}
		
		$test = Tests::where('category_id','=',intval($category_id))->first();		
		return $test;
	}

Tests {#538 ▼
  #table: "tests"
  #connection: null
  #primaryKey: "id"
  #keyType: "int"
  #perPage: 15
  +incrementing: true
  +timestamps: true
  #attributes: array:6 [▼
    "id" => 2
    "name" => "Тест по теме "О компании""
    "description" => "Описание теста"
    "category_id" => 36
    "created_at" => "0000-00-00 00:00:00"
    "updated_at" => "2018-03-19 11:03:32"
  ]
  #original: array:6 [▼
    "id" => 2
    "name" => "Тест по теме "О компании""
    "description" => "Описание теста"
    "category_id" => 36
    "created_at" => "0000-00-00 00:00:00"
    "updated_at" => "2018-03-19 11:03:32"
  ]
  #relations: []
  #hidden: []
  #visible: []
  #appends: []
  #fillable: []
  #guarded: array:1 [▶]
  #dates: []
  #dateFormat: null
  #casts: []
  #touches: []
  #observables: []
  #with: []
  #morphClass: null
  +exists: true
  +wasRecentlyCreated: false
}