String IsnullorEmpty

IsNullOrEmpty is a convenience method that enables you to simultaneously test
whether a String is null or its value is Empty. It is equivalent to the following code:

result = s == null || s == String.Empty;
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class Sample
{
    public static void Main()
    {
    string s1 = "abcd";
    string s2 = "";
    string s3 = null;
    Console.WriteLine("String s1 {0}.", Test(s1));
    Console.WriteLine("String s2 {0}.", Test(s2));
    Console.WriteLine("String s3 {0}.", Test(s3));
    }
    public static String Test(string s)
    {
    if (String.IsNullOrEmpty(s))
        return "is null or empty";
    else
        return String.Format("(\"{0}\") is not null or empty", s);
    }
}
// The example displays the following output:
//       String s1 ("abcd") is not null or empty.
//       String s2 is null or empty.
//       String s3 is null or empty.