Value of Complex Formula in Cell Returns #NAME?

public class ConcatFunction : StringsInFunction
{
    public static readonly string FunctionName = "CONCAT";
    private static readonly FunctionInfo Info;

    public override string Name
    {
        get
        {
            return FunctionName;
        }
    }

    public override FunctionInfo FunctionInfo
    {
        get
        {
            return Info;
        }
    }

    public override ArgumentConversionRules ArgumentConversionRules
    {
        get
        {
            return ArgumentConversionRules.NaryNumberFunctionConversion;
        }
    }

    static ConcatFunction()
    {
        string description = "Joins several text strings into one text string.";
        string descriptionKey = "Spreadsheet_Functions_Concatenate_Info";

        IEnumerable<ArgumentInfo> requiredArguments = new ArgumentInfo[]
        {
            new ArgumentInfo("Text",
                                "Text1, text2, ...     are 1 to 254 text items or ranges to be joined into a single text item. The text items can be text strings, numbers, or cell references.",
                                ArgumentType.Text)
        };

        IEnumerable<ArgumentInfo> optionalArguments = new ArgumentInfo[]
        {
            new ArgumentInfo("Text",
                                "Text1, text2, ...     are 1 to 254 text items or ranges to be joined into a single text item. The text items can be text strings, numbers, or cell references.",
                                ArgumentType.Text)
        };

        Info = new FunctionInfo(FunctionName, FunctionCategory.Text, description, requiredArguments, optionalArguments, 254, true, descriptionLocalizationKey: descriptionKey);
    }

    protected override RadExpression EvaluateOverride(FunctionEvaluationContext<string> context)
    {
        StringBuilder builder = new StringBuilder();

        for (int i = 0; i < context.Arguments.Length; i++)
        {
            builder.Append(context.Arguments[i]);
        }

        return new StringExpression(builder.ToString());
    }
}