Rather than having nothing come back, I would like to generate the key wrapped in braces. For example this context:

{ foo: 'foo' }

And this template:

<div>{{foo}}</div>
<div>{{bar}}</div>

Should render this output:

<div>foo</div>
<div>{{bar}}</div>

// or this...
<div>foo</div>
<div>[[bar]]</div>

// or this...
<div>foo</div>
<div>{{missing key - bar}}</div>

instead of this:

<div>foo</div>
<div></div>

The idea is to have a custom template that can be returned for keys that are missing from the given context rather than an empty string. This really helps me identify visually where certain keys in my context are missing, and which keys those are. Is this possible?