Contacts notifications some times don't contains "add" child node

[aesedepece]

The following exception occurs when a notification with type="contacts" is received and it doesn't contain a "add" child node:

Exception in thread Thread-2:
Traceback (most recent call last):
  File "/usr/lib/python2.6/threading.py", line 532, in __bootstrap_inner
    self.run()
  File "/data/waapi-api/Yowsup/connectionmanager.py", line 1077, in run
    contactJid = contactNode.getAttributeValue("jid")
AttributeError: 'NoneType' object has no attribute 'getAttributeValue'

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[aesedepece]

The following stanza is OK because contains "add":

<notification type="contacts" offline="0" from="XXXXXXXXXXX@s.whatsapp.net" id="2503128210" t="1413157578">
    <add jid="XXXXXXXXXXX@s.whatsapp.net">
    </add>
</notification>

But this one isn't because contains "remove":

<notification type="contacts" offline="0" from="XXXXXXXXXXX@s.whatsapp.net" id="3659144665" t="1416268195">
    <remove jid="XXXXXXXXXXX@s.whatsapp.net">
    </remove>
</notification>

[aesedepece]

In addition, we still need to guess what we should answer to these notifications in order to acknowledge them and not been dropped from WhatsApp servers after a while with a TWO READER THREADS ON BOARD!! exception (this happens after notifications acks were disabled by 7fabc76956c7a653a58785c7fbb01597a2c8d4df)

Am I right, @tgalal ?