Emptying BossBar flags always calls bossBarFlagsChanged, even if nothing was changed

[threefusii]

BossBar implementations calls BossBar.Listener.bossBarFlagsChanged(...) if BossBar.flags(...) accepted an empty set, even if the flags were already empty. The following program:

// Create an example HelloWorld-alike problem.
// Can be done without any underlying platform.
BossBar bar = BossBar.bossBar(Component.text("test"), 0.0F, BossBar.Color.WHITE, BossBar.Overlay.PROGRESS, Set.of());
bar.addListener(new BossBar.Listener() {
    @Override
    public void bossBarFlagsChanged(@NotNull BossBar bar, @NotNull Set<BossBar.Flag> flagsAdded, @NotNull Set<BossBar.Flag> flagsRemoved) {
        System.out.println("Changed from " + flagsAdded + " to " + flagsRemoved);
    }
});

// Works as intended. (prints only once)
bar.flags(Set.of(BossBar.Flag.CREATE_WORLD_FOG));
bar.flags(Set.of(BossBar.Flag.CREATE_WORLD_FOG));
bar.flags(Set.of(BossBar.Flag.CREATE_WORLD_FOG));
bar.flags(Set.of(BossBar.Flag.CREATE_WORLD_FOG));
bar.flags(Set.of(BossBar.Flag.CREATE_WORLD_FOG));

// Possibly broken behavior. (prints 5 times)
bar.flags(Set.of());
bar.flags(Set.of());
bar.flags(Set.of());
bar.flags(Set.of());
bar.flags(Set.of());

prints this:

Changed from [CREATE_WORLD_FOG] to []
Changed from [] to [CREATE_WORLD_FOG]
Changed from [] to []
Changed from [] to []
Changed from [] to []
Changed from [] to []

Adventure versions: Both 4.16.0 and 4.17.0-SNAPSHOT.