Resolve "500 Internal Server Error: Cherrypick commit with empty branch name"

What does this MR do?

Fixes 500 for cherry pick API with empty branch name

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides

Closes #50677 (closed)