Encode falsey values

[hyyan]

Fixes #77.

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Thanks for your pull request. It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

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[hyyan]

I signed it!

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CLAs look good, thanks!

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CLAs look good, thanks!

[hyyan]

Hey, is there a chance to merge this PR ?

[e111077]

Passed initial review. Can you please fix the conflicts and add this case to our tests?