debugging nullpointer exception at application startup

1. tables not existing
2. turning on hibernate logging and debugging
3. incomplete service and repositories
4. incomplete values in the rdbms tables
5. spring data jpa misconfiguration
6. completing service and repository classes
7. set vs list in collection mapping
8. ensuring uniqueness of collections to be returned
9. get training on 
1. spring data jpa
2. spring boot
3. testing
4. debugging
5. UML
6.