If a <driver> if configured with no <driver-class>, it will attempt to locate the driver(s) via the service loader which should find all JDBC4-compliant drivers.

When you install a non JDBC4-complicant driver as a module and no <driver-class>, the driver will not be installed. That is expected but emitting a warning that no-drivers could be found in the module would be useful to help users troubleshoot the problem.