Backend should throw an Error if someone tries to close an empty bulk process

Summary

Currently an bulk doesn't have to contain any data to be sucessfully closed. An index is created in the database and you can even search it...

Steps to reproduce

  • open a bulk
  • close it...

Which version of the software did you use ?

02475f59

What is the expected correct behavior?

It should throw an Error that is documented in the StappsCore. Something like SCEmptyBulkError...

cc: @krlwlfrt