I had a look at the mentioned classes, and the issues look valid to me.
Unfortunately, it looks like that odata4j is no longer maintained. I couldn't find any security point of contact with whom I could discuss the issue.
I see two possible mitigations here:
1. Migrate to other OData implementations (for example, see Apache Olingo).
2. Don't use org.odata4j.producer.jpa package.
I'll try to request a CVE for the issues. It may help to bring attention to the problem.
Artem