When I was making a test case for saving a project post in my ProjectRepository, this error popped up:

org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint [null]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement

Dafuq? I googled and they were talking about PK제약조건이 중복되어서 생기는 오류.

But for my case, one of my attributes (Blob contentBig) in Project class was @Column(nullable=false) and I did not put sample data for it while testing. Either allowing it to accept null values or adding sample data is the solution.