Boolean fields are not indexed after upgrade to 6.8.7 from 5.6.16

I'm trying to upgrade the org.elasticsearch:elasticsearch to 6.8.7 from 5.6.16 as part of spring boot upgrade. When trying to create index with static mappings, I have noticed no information is stored for the boolean fields in the index.

Is there any changes done how the mappings declared for boolean fields?

Using the ElasticsearchTemplate.index(IndexQuery), where the IndexQuery is built with an document object having some boolean fields

Depending on how you represent boolean values this might be relevant.