presto-main/src/main/java/io/prestosql/execution/resourcegroups/InternalResourceGroupManager.java/InternalResourceGroupManager/getConfigurationManager
class InternalResourceGroupManager:    @SuppressWarnings("ObjectEquality")
    @VisibleForTesting
    public ResourceGroupConfigurationManager<C> getConfigurationManager()
    {
        ResourceGroupConfigurationManager<C> manager = configurationManager.get();
        checkState(manager != legacyManager, "cannot fetch legacy manager");
        return manager;
    }