Adding an icon to a form dialog

I created a Dialog and changed the text. Now I am trying to change the icon in the header of the dialog.

So far I tried:

public CreateDialog() {
    // set Title for dialog
    this.setTitle("Create Class");
    // set Image for dialog. Also tried .ico file
    URL iconURL = getClass().getResource("/icons/logo.svg");
    ImageIcon icon = new ImageIcon(iconURL);
    // tried both
    // this.setIconImage(icon.getImage());
    this.getOwner().setIconImage(icon.getImage());

It always shows the red-blue IntelliJ icon.
When I am trying dialog.setIconImage nothing happens.
When I try dialog.getOwner().setIconImage I getting the full black IntelliJ icon, but still not mine.