Issue with serializeLabel method

[sandytechno1]

There is no null handing for "full" parameter

private string serializeLabel(out int length, string question, out string rest, string full = "")

if (currentBit == "C0") in above condition if full parameter is null it throws exception on below line, string data = full.Substring(offset);

What is current bit and what are all these conditions if you have any documentation around it please do share.