Exception occurs while an admin user tries to delete a 'Branch' containing active topic

Preconditions:
'Jcommune' user should exists and be added to some group in Poulpe(Registered User for ex).

Steps to reproduce:

1. Navigate to the uat.jtalk.org/jcommune,
2. Login to the system using admin/admin credential
3. Navigate to the Jcommune - Forum Structure and perform 'Create section' action
4. Create new 'TestBranch' related to the Section from step 3
5. Give all nessesary permissions to the group of 'Jcommune' user (create topic, view topic,..)
6. Navigate to the uat.jtalk.org/jcommune and login as 'Jcommune'
7. Create New topic in the 'TestBranch'
8. go to Poulpe again and try to delete TestBranch(or Section) from step 4

Actual: The admin user cannot delete Branch/Section. Exception occurs stating:

"Could not execute JDBC batch update; SQL [/* delete org.jtalks.poulpe.model.entity.PoulpeBranch */ delete from BRANCHES where BRANCH_ID=?]; constraint [null]; nested exception is org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update[SQL: 1451, 23000]"

Expected: The admin user is able to delete Branch/Section