Implements more move effects

PkmnLib.Dynamic/ScriptHandling/ScriptSet.cs

@@ -21,7 +21,7 @@ public interface IScriptSet : IEnumerable<ScriptContainer>
     /// Adds a script with a name to the set. If the script with that name already exists in this
     /// set, this makes that script stack instead. The return value here is that script.
     /// </summary>
-    ScriptContainer? StackOrAdd(StringKey scriptKey, Func<Script> instantiation);
+    ScriptContainer? StackOrAdd(StringKey scriptKey, Func<Script?> instantiation);
 
     /// <summary>
     /// Gets a script from the set using its unique name.