Vue.js version

2.1.10

Reproduction Link

https://jsfiddle.net/nymhjosc/

Steps to reproduce

Simply omit a Boolean prop and the value will be casted to false.

What is Expected?

I'd expect to have an undefined property just to know that the user didn't provide it (since it is not a required prop). Basically, I would expect both myProp and missingProp in the previous example to be the same.

What is actually happening?

When the prop is not provided its content is casted to false. Also, some other values like '' are casted to true (somewhat related to #4538) but I guess this is intended. I'm using default: undefined for now.