Avoid copying empty NBT when draining bottles

When filling a barrel from a bottle, ensured that empty NBT tags (ex: "{}") are replaced with null values and not transferred to the fluid unnecessarily. This ensures that water bottles placed in a barrel properly merge with the current contents of the barrel instead of not matching because {} != null.

src/main/java/thedarkcolour/exdeorum/blockentity/BarrelBlockEntity.java

@@ -249,6 +249,7 @@ public class BarrelBlockEntity extends ETankBlockEntity {
                     	// Transfer any extra NBT tags from other mods to the fluid
                     	 var nbt = playerItem.getTag().copy();
                     	 nbt.remove("Potion");
+                         if (nbt.isEmpty()) nbt = null;
                     	 fluid = new FluidStack(Fluids.WATER, 250, nbt);
 
                         if (this.tank.fill(fluid, IFluidHandler.FluidAction.SIMULATE) > 0) {