avoid attribute errors when accessing connection

[zvictor]

Thank you for publishing ddp-apollo! Even though I am not using it directly, I managed to solve a humongous old bug in my application while studying how you managed to invoke dpp calls (#190).

Things were going pretty well until I started getting errors while trying to call Meteor's verifyEmail.
The problem was that connection: null results in (null).id at accounts_server.js:855:

https://github.com/meteor/meteor/blob/573c9dc478b15df70fa26c4a753d62077df1b066/packages/accounts-base/accounts_server.js#L854-L856

Setting connection: {} solves the issue to me, so I would like to know if there is any reason to keep null instead.

[Cliffzz]

Thank you! Looks good to me, I'm not a 100% sure why it was done this way before.