We where creating a custom master page to replace the OOB mysite.master. Our plan was to use one common master for all usage scenarios. Applying our master page we got a server error:
Object reference not set to an instance of an object.
in the method:
I had no clue what the issue was before i checked the implemntation of the OnInit() method using Reflector.
I turns out that pages inheriting from MySitePublicWebPartPage MUST have the content placeholder "PlaceHolderLeftNavBar" defined - it's hardcoded and NO check on null :-(.