HTTP 500 error with DreamCompute

When I set up a connection to DreamCompute, I get an HTTP 500 error during `client.images().listMembers("")`

I'm using Endpoint URL `https://iad2.dream.io:5000/v2.0`, with an `Openstack Auth v2` credential.

```
ServerResponseException{message=Internal Server Error, status=500, status-code=INTERNAL_SERVER_ERROR}
at org.openstack4j.core.transport.HttpExceptionHandler.mapException(HttpExceptionHandler.java:40)
at org.openstack4j.core.transport.HttpExceptionHandler.mapException(HttpExceptionHandler.java:23)
at org.openstack4j.core.transport.HttpEntityHandler.handle(HttpEntityHandler.java:51)
at org.openstack4j.connectors.okhttp.HttpResponseImpl.getEntity(HttpResponseImpl.java:69)
at org.openstack4j.openstack.internal.BaseOpenStackService$Invocation.execute(BaseOpenStackService.java:225)
at org.openstack4j.openstack.internal.BaseOpenStackService$Invocation.execute(BaseOpenStackService.java:207)
at org.openstack4j.openstack.image.internal.ImageServiceImpl.listMembers(ImageServiceImpl.java:189)
at jenkins.plugins.openstack.compute.internal.Openstack.sanityCheck(Openstack.java:752)
at jenkins.plugins.openstack.compute.JCloudsCloud$DescriptorImpl.doTestConnection(JCloudsCloud.java:510)
```

It looks like `Throwable.getMessage()` doesn't tell us quite enough about the error from the API. How can I get more information about what went wrong?