private String toString(Agent agent) {
        return switch (agent) {
            case operator -> "operator";
            case application -> "application";
            case system -> "system";
            case nodeAdmin -> "nodeAdmin";
            case DirtyExpirer -> "DirtyExpirer";
            case HostCapacityMaintainer -> "DynamicProvisioningMaintainer";
            case HostResumeProvisioner -> "HostResumeProvisioner";
            case FailedExpirer -> "FailedExpirer";
            case InactiveExpirer -> "InactiveExpirer";
            case NodeFailer -> "NodeFailer";
            case NodeHealthTracker -> "NodeHealthTracker";
            case ProvisionedExpirer -> "ProvisionedExpirer";
            case Rebalancer -> "Rebalancer";
            case ReservationExpirer -> "ReservationExpirer";
            case RetiringOsUpgrader -> "RetiringUpgrader";
            case RebuildingOsUpgrader -> "RebuildingOsUpgrader";
            case SpareCapacityMaintainer -> "SpareCapacityMaintainer";
            case SwitchRebalancer -> "SwitchRebalancer";
            case HostEncrypter -> "HostEncrypter";
            case ParkedExpirer -> "ParkedExpirer";
            case HostFlavorUpgrader -> "HostFlavorUpgrader";
        };
    }
Returns the event type, or null if this event type should be ignored
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/persistence/NodeSerializer.java