A astral character safe first char method for C#

FirstCharUtf32.cs

static class FirstCharUtf32 {
    public static bool FirstChar(string Str, out int First) {
        bool SUCCESS_INDICATOR;
        int len = Str.Length;
        if (len > 0) {
            First = Str[0];
            if (char.IsSurrogate((char)First)) {
                if (SUCCESS_INDICATOR = char.IsSurrogatePair(Str, 0)) {
                    First = char.ConvertToUtf32((char)First, Str[1]);
                }
            } else {
                SUCCESS_INDICATOR = true;
            }
        } else {
            First = 0;
            SUCCESS_INDICATOR = false;
        }

        return SUCCESS_INDICATOR;
    }

    public static void TestFirstChar(char[] chars) {
        int first;
        string s = new string(chars);
        bool success = FirstChar(s, out first);
        string hex = ConvertStringToHex(s);
        System.Console.WriteLine("First Char of {0} is {1:x} \t= {2}", hex, first, success);
    }

    public static void Main(string[] args) {
        char c1 = (char)0xd800;
        char c2 = (char)0xdc00;
        TestFirstChar(new char[] {c1, c2});
        TestFirstChar(new char[] {c1});
        TestFirstChar(new char[] {c2});
        TestFirstChar(new char[] {});
        TestFirstChar(new char[] {'a'});
    }
    
    public static string ConvertStringToHex(string str)
    {
        System.Text.StringBuilder hex = new System.Text.StringBuilder(str.Length * 6 + 2);
        hex.Append('"');
        foreach (int codeUnit in str) {
            hex.AppendFormat("\\u{0:X2}", codeUnit);
        }
        hex.Append('"');
        return hex.ToString();
    }
}