When I search with only birthData in fhir I am getting results. 

For example: `http://localhost:8080/hapi-fhir-jpaserver/fhir/Patient?_pretty=true&birthdate=2020-03-16` will return patient who has birthdate as `2020-03-16`.

When I am searching with `_content` I am not getting any results. Something like this: 

```
http://localhost:8080/hapi-fhir-jpaserver/fhir/Patient?_content=2019-09-05

```