null/nil values for a custum functoid

Hi,

I just tried to create a custom functoid like the coalesce function in SQL. A function returning the first non-null value. But I experience the following problem: When I connect strings, it works fine, but if I connect a value mapper my function as a parameter, and the value mapper does not result in a value, my function does not return any value, even if another parameter to my function has a value. What does the value mapper generate on false? nil? nothing? it seems that the function afterwards is not called at all.

 Any ideas?

 
using System;
using System.Collections.Generic;
using System.Text;
using Microsoft.BizTalk.BaseFunctoids;
using System.Reflection;

namespace TTBiztalkFunctoids
{
    public class CoalesceFunctoid : BaseFunctoid
    {
        public CoalesceFunctoid()
            : base() {

            this.ID = 7000;
            this.Category = FunctoidCategory.String;

            // this to get the resources embedded in the resx file,
            // call GetExecutingAssembly because the resource is compiled and embedded into the DLL.
            SetupResourceAssembly("TTBiztalkFunctoids.Resources", Assembly.GetExecutingAssembly());

            SetDescription("Coalesce_Description");
            SetTooltip("Coalesce_Tooltip");
            SetBitmap("Coalesce_Icon");             // must be an embedded BITMAP, not icon!!!
            SetName("Coalesce_Name");
           
            AddScriptTypeSupport(ScriptType.CSharp);

            //this function can accept variable inputs. The overidden function "GetInlineScriptBuffer" will
            //provide inline script code for various number of inputs.
            this.HasVariableInputs = true;

            //Set the minimum number of parameters to be 1
            this.SetMinParams(1);

            //// this method call tells the mapper what function to call, when functoid is deployed to GAC.
            //SetExternalFunctionName(GetType().Assembly.FullName,
            //    "TTBiztalkFunctoids.Coalesce", "Coalesce");

            // define output and input connection types..
            this.OutputConnectionType = ConnectionType.AllExceptRecord;
            AddInputConnectionType(ConnectionType.AllExceptRecord);

        }

        //this overidden function provides inline code for various number of inputs.
        protected override string GetInlineScriptBuffer(ScriptType scriptType, int numParams, int functionNumber) {
            if (ScriptType.CSharp == scriptType) {
                StringBuilder builder = new StringBuilder();

                builder.Append("public string Coalesce(");

                for (int i = 0; i < numParams; i++) {
                    if (i > 0) {
                        builder.Append(", ");
                    }

                    builder.Append("string param");
                    builder.Append(i.ToString());
                }

                builder.Append(")\n");
                builder.Append("{\n");

                builder.Append("   System.Collections.ArrayList listStrings = new System.Collections.ArrayList();\n");

                for (int j = 0; j < numParams; j++) {
                    builder.Append("   listStrings.Add(param");
                    builder.Append(j.ToString());
                    builder.Append(");\n");
                }

                builder.Append("   foreach (string s in listStrings)\n");
                builder.Append("   {\n");
                builder.Append("       if (s!=null)\n");
                builder.Append("       {\n");
                builder.Append("           return s;\n");
                builder.Append("       }\n");
                builder.Append("   }\n");
                builder.Append("   return null;\n");
                builder.Append("}\n");

                return builder.ToString();
            } else {
                return "";
            }
        }

        //public string Coalesce(params string[] inputs) {
        //    foreach (string input in inputs) {
        //        if (input != null) return input;
        //    }
        //    return null;
        //}
    }

}