Type checker doesn't detect usage of optional properties

[dselman]

Hello {{name}}! 

Today is **{{% return now.toISOString() %}}**.

{{last}}

namespace [email protected]

@template
concept HelloWorld {
    o String name
    o String last optional
}

Context

This is detected if last is used in a TS expression, but not as a simple variable.

Expected Behavior

Should raise an error that {{last}} is being used and is an optional.

Actual Behavior

Runtime failure:

Error: No values found for path '$['last']' in data [object Object].

Possible Fix

Steps to Reproduce

Existing issues

• Stack Overflow issues
• GitHub Issues

Context

Your Environment

• Version used:
• Environment name and version (e.g. Chrome 39, node.js 5.4):
• Operating System and version (desktop or mobile):
• Link to your project:

[Vinyl-Davyl]

Hello @dselman permit me to work on this issue