Fixes issue where HeldItem string in PokemonBuilder could be empty.

PkmnLibSharp/Battling/PokemonBuilder.cs

@@ -146,7 +146,7 @@ namespace PkmnLibSharp.Battling
             PopulateUninitialized(species, forme!, random);
 
             Item? heldItem = null;
-            if (HeldItem != null)
+            if (HeldItem != null && !string.IsNullOrWhiteSpace(HeldItem))
             {
                 if (!Library.StaticLibrary.ItemLibrary.TryGet(HeldItem, out heldItem))
                 {