tags "if" ReferenceError: [field] is not defined

I ran into a problem where the json returned from an api, then sent to Tempo would cause an error because 2 fields had similar names.

The fields: price and compareToPrice

compareToPrice is not always returned as a field but was being used in the template to display html if it did:

{% if compareToPrice %}
do stuff
{% endif %}

What happens is that Tempo runs line 766:

expr = expr.replace(new RegExp(member_regex, 'gi'), function (match) {
    return 'i.' + match;
});

compareToPrice wouldn't exist as a field but 'price' does so the above returns: compareToi.Price

Might be possible to fix by changing regex? I don't know enough to do anything there so I just put the eval in a try/catch block that returns '' if it fails.