I would like to have a BoP sapling drop from my block if it is also installed. I think I have done everything and I cannot pinpoint the problem, which is the error in the logs that appears when joining a world:
 

[Worker-Main-11/ERROR] [ne.mi.co.ForgeHooks/]: Couldn't parse element loot_tables:grasses:blocks/leaves_block
com.google.gson.JsonSyntaxException: Expected name to be an item, was unknown string 'biomesoplenty:magic_sapling'

My code:
 

LootItemConditions.CONDITIONS.register(modEventBus);

public class LootItemConditions {

    public static final DeferredRegister<LootItemConditionType> CONDITIONS =
            DeferredRegister.create(Registries.LOOT_CONDITION_TYPE, Grasses.MOD_ID);

    public static final RegistryObject<LootItemConditionType> IS_MOD_LOADED =
            CONDITIONS.register("is_mod_loaded", () -> new LootItemConditionType(new IsModLoaded.ConditionSerializer()));
}

public class IsModLoaded implements LootItemCondition {

    private final boolean exists;
    private final String modID;

    public IsModLoaded(String modID) {
        this.exists = ModList.get().isLoaded(modID);
        this.modID = modID;
    }

    @Override
    public LootItemConditionType getType() {
        return LootItemConditions.IS_MOD_LOADED.get();
    }

    @Override
    public boolean test(LootContext context) {
        return this.exists;
    }

    public static LootItemCondition.Builder builder(String modid) {
        return () -> new IsModLoaded(modid);
    }

    public static class ConditionSerializer implements Serializer<IsModLoaded> {
        @Override
        public void serialize(JsonObject json, IsModLoaded instance, JsonSerializationContext ctx) {
            json.addProperty("modid", instance.modID);
        }

        @Override
        public IsModLoaded deserialize(JsonObject json, JsonDeserializationContext ctx) {
            return new IsModLoaded(GsonHelper.getAsString(json, "modid"));
        }
    }
}

protected LootTable.Builder createLeavesDropsWithModIDCheck(Block selfBlock, Item sapling, Property<?>[] properties, String modIDToCheck, float... chances) {
        CopyBlockState.Builder blockStateCopyBuilder = CopyBlockState.copyState(selfBlock);

        for(Property<?> property : properties) {
            blockStateCopyBuilder.copy(property);
        }

        return LootTable.lootTable()
                .withPool(LootPool.lootPool().setRolls(ConstantValue.exactly(1.0F))
                        .add(LootItem.lootTableItem(selfBlock)
                                .when(HAS_SHEARS_OR_SILK_TOUCH)
                                .apply(blockStateCopyBuilder)))
                .withPool(LootPool.lootPool().setRolls(ConstantValue.exactly(1.0F))
                        .add(this.applyExplosionCondition(selfBlock, LootItem.lootTableItem(sapling))
                            .when(IsModLoaded.builder(modIDToCheck)))
                        .when(BonusLevelTableCondition.bonusLevelFlatChance(Enchantments.BLOCK_FORTUNE, chances))
                        .when(HAS_NO_SHEARS_OR_SILK_TOUCH))
                .withPool(LootPool.lootPool().name("sticks").setRolls(ConstantValue.exactly(1.0F))
                        .add(this.applyExplosionDecay(selfBlock, LootItem.lootTableItem(Items.STICK).
                                        apply(SetItemCountFunction.setCount(UniformGenerator.between(1.0F, 2.0F))))
                                .when(BonusLevelTableCondition.bonusLevelFlatChance(Enchantments.BLOCK_FORTUNE, NORMAL_LEAVES_STICK_CHANCES))
                                .when(HAS_NO_SHEARS_OR_SILK_TOUCH)));

    }

I don't know. Am I making a mistake somewhere? Am I forgetting something? Should there be something else?

This is sad. Over 3300 people have checked the thread and no one is able to help or give any ideas :(.