Problems with Capabilities

[GrigLog]

First of all, I am unable to subscribe to AttachCapabilitiesEvent. In theory, it should be as simple as follows:
 

@Mod.EventBusSubscriber
public class CapabilityEvents {
    @SubscribeEvent
    public void playerCapability(final AttachCapabilitiesEvent<Entity> event){
        Soul.LOGGER.info("attach capabilities");
        if (event.getObject() instanceof PlayerEntity) {
            event.addCapability(new ResourceLocation("soul", "soul"), new SoulProvider());
        }
    }
}

, but it does not get called. Secondly, I cant really understand what CapabilityProvider is, where it is used and what I should return in method implementation. From different sources in the internet Ive made the following class:

public class SoulProvider implements ICapabilityProvider {
    @CapabilityInject(ISoul.class)
    public static Capability<ISoul> SOUL_CAP = null;
    private LazyOptional<ISoul> instance = LazyOptional.of(() -> new DefaultSoul());

    @Nonnull
    @Override
    public <T> LazyOptional<T> getCapability(@Nonnull Capability<T> cap, @Nullable Direction side) {
        return cap == SOUL_CAP ? instance.cast() : LazyOptional.empty();
    }

    @Nonnull
    @Override
    public <T> LazyOptional<T> getCapability(@Nonnull Capability<T> cap) {
        return cap == SOUL_CAP ? instance.cast() : LazyOptional.empty();
    }
}

, but it looks like a total nonsense. Forge documentation is a cruel joke and doesnt contain any useful info/examples...

Edited June 11, 2021 by GrigLog
SOUL_CAP::getDefaultInstance was not working, you have to specify the default implementation here