public class TodoDetailsPart {

	@Inject
	ESelectionService s;

	@Inject
	public void updateSelection(@Optional
			@Named(IServiceConstants.ACTIVE_SELECTION) Person p) {
		System.out.println(" value " + p);
	}

	@PostConstruct
	public void createPartControls(Composite parent) {
		parent.setLayout(new GridLayout(1, false));

		btnLoadData = new Button(parent, SWT.NONE);
		btnLoadData.addSelectionListener(new SelectionAdapter() {
			@Override
			public void widgetSelected(SelectionEvent e) {
				System.out.println("sending null selection");
                                // set new selection to NULL -> no event propagated to #updateSelection().
				s.setSelection(null);
			}
		});
       ...
}}

public class MySelectionConstants {
    
    /**
     * Use this object to remove the current selection.
     */ 
    public static final Object NULL_OBJECT = new Object();
}

    @Inject
    public void updateSelection(@Optional
            @Named(IServiceConstants.ACTIVE_SELECTION) Object sel) {
        
        if (sel == MySelectionConstants.NULL_OBJECT)
            ; // Handle the removal of the active selection

        // Type check!
        else if (sel instanceof Person) {
            // You business logic
            Person p = (Person) sel;
            System.out.println(" value " + p);
        }
    }

    ...
    public static final Person NULL_PERSON = new Person();
}


    @Inject
    public void updateSelection(@Optional
            @Named(IServiceConstants.ACTIVE_SELECTION) Person sel) {
        
        if (sel == MySelectionConstants.NULL_PERSON)
            ; // Handle the removal of the active selection

        // No type check
        else {
            ...

selectionService.setSelection(new Person[] {});