Help developers by indicating undefined data in debug mode

[vparpoil]

It would be great to implement a debug mode that could be enabled by default in development mode (via process.env or Meteor.isDevelopment ?) that adds logging messages when a variable is not defined in a template.

As an example the following code

<template name="MyTemplate">
   <div>
    {{title}}
  </div>
</template>

could raise console info messages on render when title is not defined in Template.instance().data or not defined in template helpers or when the helper return an undefined value

I think this feature could be helpful for developers, specially when refactoring code

Do you think it would be doable without too much effect on performance ? Maybe this could be done with custom code outside of blaze core ?