public String getCoordinatorSystemNameOrNull() {
    return Optional.ofNullable(get(JOB_COORDINATOR_SYSTEM)).orElseGet(() -> getDefaultSystem().orElse(null));
  }
Gets the System to use for reading/writing the coordinator stream. Uses the following precedence.

1. If job.coordinator.system is defined, that value is used.
2. If job.default.system is defined, that value is used.
3. None
samza-core/src/main/java/org/apache/samza/config/JobConfig.java