fix in operator

[TheChoconut]

Summary

When using the in operator inside a template literal, if the object is null, compiler will fail.

For example:
{{ 'yes' if myOption in preferences else 'no' }} fails to render if preferences is not in context map.

In Python's Jinja2 render, it is possible to setup the compiler to make this render to no.
I would expect this not to fail if throwOnUndefined is set to false. If this is not the expected behavior, would like to hear what would be the option to support this.

Also would like to add a test for this but I am not sure what would be the correct location.

This PR fixes the compiler issue.

Checklist

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• Proposed change helps towards purpose of this project.
• Documentation is added / updated to describe proposed change.
• Tests are added / updated to cover proposed change.
• Changelog has an entry for proposed change (if user-facing fix or feature).