问使用一对一数据库“从空值创建默认值”Laravel更新错误

EN

    class Telepon extends Model
{
    protected $table      = 'telepon';
    protected $primaryKey = 'id_siswa';
    protected $fillable   = [
        'id_siswa',
        'nomor_telepon',
    ];

    public function siswa() {
        return $this->belongsTo('App\Siswa', 'id_siswa');
    }

public function telepon() {
    return $this->hasOne('App\Telepon', 'id_siswa');
}

public function update(Siswa $siswa, SiswaRequest $request){
        $input = $request->all();

        $siswa->update($input);

        $telepon = $siswa->telepon;
        $telepon->nomor_telepon = $request->input('nomor_telepon');
        $siswa->telepon()->save($telepon);

        $siswa->hobi()->sync($request->input('hobi_siswa'));

        return redirect('siswa');
    }