ERR wrong number of arguments for 'setnx' command #2751

When calling IDatabase.StringSet with when=When.NotExists and keepTtl=true, you are calling the "SETNX" command and also passing the KEEPTTL option, which is not supported. This should be updated to use the "SET" command with the "NX" and "KEEPTTL" options instead.

Example call:
IDatabase db = ...;
bool result = db.StringSet("key", "value", null, true, When.NotExists);