Convert list of strings into single string value; exclude all null list members

I am a little confused as there are no nulls but, not to mention just create the all string directly (unless you are trying to understand the concept :

List<string> slist = new string[]{'abc','bcd','cde','def','efg'};

slist.remove(null);
string allstring = string.join(sList,',');

Is a simplified version of your code