SiteDefinition should handle nullable SecondaryContactLogin

[SubPointSupport]

Hi, When I am provisioning a new SiteDefinition if I do not populate the SecondaryContactLogin the code throws and exception.

The issues is with the SSOM SiteModelHandler.cs#L98 and #l125. It needs to have a check on that call to ensure that the SecondaryContactLogin is not null or empty.

Community feedback:
https://www.yammer.com/spmeta2feedback/#/threads/show?threadId=707563888