Add condition to not populate string value if it's empty

[FikriMilano]

IMPORTANT: All PRs must be linked to an issue (except for extremely trivial and straightforward changes).

Fixes #2520

Description Add condition to not populate string value if it's empty

Alternative(s) considered N/A

Type Bug fix

Screenshots (if applicable)

https://github.com/google/android-fhir/assets/62053304/afe018e0-32c7-43a3-9e4f-393f96b7e9aa

Checklist

• [x] I have read and acknowledged the Code of conduct.
• [x] I have read the Contributing page.
• [x] I have signed the Google Individual CLA, or I am covered by my company's Corporate CLA.
• [ ] I have discussed my proposed solution with code owners in the linked issue(s) and we have agreed upon the general approach.
• [x] I have run ./gradlew spotlessApply and ./gradlew spotlessCheck to check my code follows the style guide of this project.
• [x] I have run ./gradlew check and ./gradlew connectedCheck to test my changes locally.
• [x] I have built and run the demo app(s) to verify my change fixes the issue and/or does not break the demo app(s).