Append commas only if strings are not null or empty

If you want to remove the empty or null string you have to filter the array used in the join method:

var array = new[] { address1, address2, city, country, postalCode };
string fullAddress = string.Join(",", array.Where(s => !string.IsNullOrEmpty(s)));

If we make city="" the we have Address1,Address2,Country,00000