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I am developing a JavaFX application which uses the Apache Felix OSGi framework. I have an issue with firing custom events. Whenever I try to fire a custom event, the exception java.lang.IllegalArgumentException: EventType "ADD_SENSOR" with parent "EVENT" already exists (stacktrace is shown below) is thrown.

Caused by: java.lang.IllegalArgumentException: EventType "ADD_SENSOR"with parent "EVENT" already exists
 at javafx.event.EventType.register(EventType.java:186)
 at javafx.event.EventType.<init>(EventType.java:128)
 at swt6.componentmanager.gui.event.AddSensorEvent.<clinit>(AddSensorEvent.java:8)

The code firing the event is shown below.

private void onAddSensor(ActionEvent event) 
 AddSensorEvent addSensorEvent = new AddSensorEvent(
 this.typeComboBox.getValue(),
 this.nameInput.getText(),
 this.descriptionInput.getText()
 );
 this.addButton.fireEvent(addSensorEvent);

 // close the window
 ((Stage) this.getScene().getWindow()).close();

The class AddSensorEvent, which also manages the EventType instance via a public static final field, is illustrated below, too.

public class AddSensorEvent extends Event 
 public static final EventType<AddSensorEvent> ADD_SENSOR_EVENT_TYPE =
 new EventType<>(EventType.ROOT, "ADD_SENSOR");

 private final SensorFactory sensorFactory;
 private final String sensorName;
 private final String sensorDescription;

 public AddSensorEvent(SensorFactory sensorFactory, String sensorName, String sensorDescription) 
 super(ADD_SENSOR_EVENT_TYPE);

 this.sensorFactory = sensorFactory;
 this.sensorName = sensorName;
 this.sensorDescription = sensorDescription;
 

 public SensorFactory getSensorFactory() 
 return this.sensorFactory;
 

 public String getSensorName() 
 return this.sensorName;
 

 public String getSensorDescription() 
 return this.sensorDescription;
 

The application is a port of an application using the Java module system, which was introduced in Java 9, and it works fine when using the module system.

I tried following this, this and this issues, but none of the provided solutions worked for me.

Thank you for your help!