[Merge] ~nteodosio/software-properties:initialize-pin into software-properties:ubuntu/master

[Sebastien Bacher]

Review: Approve

Thanks, that should at least fix the exception until we work on a proper solution to display an explanation to the user in those cases
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https://code.launchpad.net/~nteodosio/software-properties/+git/software-properties/+merge/436589
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