Compiler: v-on access _cache in hoisted element outside render function if handler is empty

[rhengles]

Version

3.0.0-rc.3

Reproduction link

https://jsbin.com/rafugesite/edit?html,js,console,output

Steps to reproduce

sometimes you create a v-on:event="" while developing but forget to call anything inside the event handler. When the handler is empty, the element is hoisted and that generates a code that tries to access the "_cache" variable outside the render(_ctx, _cache) function.

This causes an error that is not easy to understand.

What is expected?

Compile without error (empty handler doesn't do anything), or maybe print a warning "empty v-on handler found"

What is actually happening?

ReferenceError: _cache is not defined