Fixes SemverDialects: NoMethodError: undefined method `<=' for nil:NilClass

What does this MR do?

Fixes SemverDialects: NoMethodError: undefined method `<=' for nil:NilClass

Adds a check for empty interval.

What are the relevant issue numbers?

gitlab-org/gitlab#438859 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for this project, if necessary
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Security reports checked/validated by reviewer