Handle when C# calls a script function with null as parameter

Upsilon/BaseTypes/ScriptFunction/ScriptRuntimeFunction.cs

@@ -46,7 +46,12 @@ namespace Upsilon.BaseTypes.ScriptFunction
                 {
                     var parameter       = option.Parameters[index];
                     var parameterSymbol = ((UserDataVariableSymbol) parameter.VariableSymbol);
-                    var parameterType   = variables[index].GetType();
+                    var v = variables[index];
+                    if (v == null)
+                    {
+                        continue;
+                    }
+                    var parameterType   = v.GetType();
                     if (parameterSymbol.BoundTypeDefinition != null)
                     {
                         var validSymbol =