fix multiple JDBC libraries bug

[marcel-richter]

I have tried to write a unit test but failed because of my poor ruby knowledge.
I guess testing this particular line is not total straight forward and requires some kind of mock.

[cla-checker-service]

❌ Author of the following commits did not sign a Contributor Agreement:
f435b04

Please, read and sign the above mentioned agreement if you want to contribute to this project

[marcel-richter]

I have signed the contributor agreement several times. The check doesn't get green. Don't know which magic trick this requires...