How to store boolean value or empty-able value in Index Connector of Kibana Alerts?

Hi thanks for the lib! I see the {{state.isTriggered}} is a boolean. However, I cannot write down that format:

If I use "{{state.isTriggered}}", then the document fail to index, because boolean fields cannot accept string values.

In addition, for values with type date, it seems that, when it is empty, the "" will fail to index?

Thanks!

This seems like a bug to me. Can you post it here?