Add notNull to intervalTime in Lab. Null is apparently valid for

What does this mr do?

Fix creating invalid labs that break the lab overview

Actions taken to fix bug

@min does not mean: not null...

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made and the bug I fixed.
• A test was created to test the bug.
• I have updated the documentation accordingly.
• I adhere to the style guide.