Lucid hasOne relation foreign key is undefined

[farshadfahimi]

I have a model like below with the simple relation

class User extends Model {
  parent() {
    return this.hasOne('App/Models/Car', 'id', 'test_id')
  }
}

the question is in the adonisjs Model in the belongTo method I'm logging the foreignkey like below

/**
   * Returns an instance of @ref('BelongsTo') relation
   *
   * @method belongsTo
   *
   * @param  {String|Class}  relatedModel
   * @param  {String}        primaryKey
   * @param  {String}        foreignKey
   *
   * @return {BelongsTo}
   */
  belongsTo (relatedModel, primaryKey, foreignKey) {
    relatedModel = typeof (relatedModel) === 'string' ? ioc.use(relatedModel) : relatedModel
console.log(foreignKey, relatedModel.foreignKey)
    primaryKey = primaryKey || relatedModel.foreignKey
    foreignKey = foreignKey || relatedModel.primaryKey

    return new BelongsTo(this, relatedModel, primaryKey, foreignKey)
  }

but the first params I mean foreignKey return undefined but the relatedModel.foreignKey return user_id.
and as you can see I'm passing the foreignKey to the relation.