[Type verification] What is the expectation if user's API call sent wrong type? Such as `adult = "A String False"`.

For example, if in here, user sent API call that `adult = "A String False"`

https://github.com/google/shoptimizer/blob/a9fff3ac203e39480dff7585fa37b999fbe7470e/shoptimizer_api/optimizers_builtin/adult_optimizer.py#L89

Then in here the UT will fail, as shoptimizer will send string "False" directly outside.
https://github.com/google/shoptimizer/blob/a9fff3ac203e39480dff7585fa37b999fbe7470e/shoptimizer_api/optimizers_builtin/adult_optimizer_test.py#L273

Because in Python3, `if not "any string" `its value will be `False` in `boolean`. Then this will cause all these two `if` being passed
1. Passed
https://github.com/google/shoptimizer/blob/a9fff3ac203e39480dff7585fa37b999fbe7470e/shoptimizer_api/optimizers_builtin/adult_optimizer.py#L92
2. Passed
https://github.com/google/shoptimizer/blob/a9fff3ac203e39480dff7585fa37b999fbe7470e/shoptimizer_api/optimizers_builtin/adult_optimizer.py#L101

Then shoptimizer don't think its adult field need to change or santinize.

Just ask, is this phenomenon within the expectation?