NPE for Correction requests without attached bundles or bitstreams

[olli-gold]

Describe the bug
Correction requests cannot be approved when they do not contain a bitstream (which may happen for bibliographic reference items without any bitstreams). If you try it, an NPE is happening.

To Reproduce
Steps to reproduce the behavior:

1. Create an item without a bitstream in a collection, which has an approval workflow and a correction request
2. Approve that item
3. Create a correction request for this item
4. Try to approve the correction request

Expected behavior
The approval should work without problems

Related work
None I am aware of