Problem with sync birthday field with Yandex CardDav

[jean-helsinki]

After migrate to new davX version i found regression with sync birthday field in contacts.
Debug info: https://paste.centos.org/view/4ae56b2b

[rfc2822]

@jean-helsinki Hi,

Can you please provide details about the problem so that we can reproduce it and have a look at it?

[jean-helsinki]

@rfc2822 hi,
On my Yandex account in contacts book i have profiles with filled birthdays.
After migrate to new phone and sync with new davX version, contact profiles sync’ed,
but birthdays on phone book is empty.
With some older version (i not remember) birthdays sync successufuly.

[rfc2822]

I have just tried and found that

1. Yandex uses an incorrect format for birthdays without year (BDAY:--MMDD as vCard 3, which is invalid). So birthdays without year won’t be synchronized from Yandex to DAVx5.
2. Some old contacts have a birthday in the Web interface details, but not in the Web interface overview. When syncing those contacts, Yandex does not transmit a birthday.
3. When I set the birthday in the Web interface again and then sync, birthdays are working…

So it seems that Yandex’ birthday handling is not very consistent. If there are any problems, please provide exact steps to reproduce and ideally a test account.