C#分隔字符串时遭遇空值

//数组转换成字符串，字符串切割成数组.

string[] array = new[] {"1m2", "", "ww", "mm", "acas,"};//集合初始化.

string arrayString = string.Join(",", array);//把数组按指定的分隔符转换成字符串.

int count = arrayString.Count(s => s == ‘a‘);//计算某个字符在字符串中出现的次数.

string[] shuzu = arrayString.Split(‘,‘);//把string字符串按指定的字符切割成数组.

//处理各种情况多余的逗号.
string zifu = ",1,2,,3,,,4,5,6,,7,8,,,9,";
string a = Regex.Replace(zifu, ",{2,}", ",");//将连续两个及以上的逗号替换成一个逗号.
string b = Regex.Replace(zifu, "^\\,|(\\,{2,})|\\,$", "");//开头和结尾不能是中英文逗号，不能有连续中英文逗号.
string c = Regex.Replace(zifu, "^\\,|\\,$", "");//不能以逗号开头或结尾.
string d = Regex.Replace(a, "^\\,|\\,$", "");//不能以逗号开头或结尾.

string zifu1 = ",1,2,3,";//以逗号开头和结尾.
string e = Regex.Replace(zifu1, "^\\,&\\,$", "");//不能以逗号开头和结尾，正则无效.
string f = Regex.Replace(zifu1, "^\\,|\\,$", "");//不能以逗号开头或结尾，满足.

string zifu2 = ",1,2,3";//以逗号开头.
string i = Regex.Replace(zifu2, "^\\,&\\,$", "");//不能以逗号开头和结尾，正则无效.
string j = Regex.Replace(zifu2, "^\\,|\\,$", "");//不能以逗号开头或结尾，满足.

string zifu3 = "1,2,3,";//以逗号结尾.
string g = Regex.Replace(zifu3, "^\\,&\\,$", "");//不能以逗号开头和结尾，正则无效.
string h = Regex.Replace(zifu3, "^\\,|\\,$", "");//不能以逗号开头或结尾，满足.