SQL CLR User Defined Function (C#) adds null character (\0) in between every existing character in String being returned - clr

Question

This one has kept me stumped for a couple of days now.
It's my first dabble with CLR & UDF ...
I have created a user defined function that takes a multiline String as input, scans it and replaces a certain line in the string with an alternative if found. If it is not found, it simply appends the desired line at the end. (See code)
The problem, it seems, comes when the final String (or Stringbuilder) is converted to an SqlString or SqlChars. The converted, returned String always contains the Nul character as every second character (viewing via console output, they are displayed as spaces).
I'm probably missing something fundamental on UDF and/or CLR.
Please Help!!
Code (I leave in the commented Stringbuilder which was my initial attempt... changed to normal String in a desperate attempt to find the issue):
[Microsoft.SqlServer.Server.SqlFunction]
[return: SqlFacet(MaxSize = -1, IsFixedLength = false)]
//public static SqlString udf_OmaChangeJob(String omaIn, SqlInt32 jobNumber) {
public static SqlChars udf_OmaChangeJob(String omaIn, SqlInt32 jobNumber) {
if (omaIn == null || omaIn.ToString().Length <= 0) return new SqlChars("");
String[] lines = Regex.Split(omaIn.ToString(), "\r\n");
Regex JobTag = new Regex(#"^JOB=.+$");
//StringBuilder buffer = new StringBuilder();
String buffer = String.Empty;
bool matched = false;
foreach (var line in lines) {
if (!JobTag.IsMatch(line))
//buffer.AppendLine(line);
buffer += line + "\r\n";
else {
//buffer.AppendLine("JOB=" + jobNumber);
buffer += ("JOB=" + jobNumber + "\r\n");
matched = true;
}
}
if (!matched) //buffer.AppendLine("JOB=" + jobNumber);
buffer += ("JOB=" + jobNumber) + "\r\n";
//return new SqlString(buffer.ToString().Replace("\0",String.Empty)) + "blablabla";
// buffer = buffer.Replace("\0", "|");
return new SqlChars(buffer + "\r\nTheEnd");
}

Answer 1

I know in my experiences, the omaIn parameter should be of type SqlString and when you go to collect its value/process it, set a local variable:
string omaString = omaIn != SqlString.Null ? omaIn.Value : string.empty;
Then when you return on any code path, to rewrap the string in C#, you'd need to set
return omaString == string.empty ? new SqlString.Null : new SqlString(omaString);
I have had some fun wrestling matches learning the intricate hand-off between local and outbound types, especially with CLR TVFs.
Hope that can help!