String - IsNullOrWhiteSpace

Indicates whether a specified string is null, empty, or consists only of white-space characters.

Try it

public static void Main()
{
	string[] values = { null, String.Empty, "ABCDE", 
                      new String(' ', 20), "  \t   ", 
                      new String('\u2000', 10) };
	
	foreach (string str in values)
	{
		// C# Extension Method: String - IsNullOrWhiteSpace
		Console.WriteLine(str.IsNullOrWhiteSpace());
	}
}

View Source
using System;

public static partial class Extensions
{
    /// <summary>
    ///     Indicates whether a specified string is null, empty, or consists only of white-space characters.
    /// </summary>
    /// <param name="value">The string to test.</param>
    /// <returns>true if the  parameter is null or , or if  consists exclusively of white-space characters.</returns>
    public static Boolean IsNullOrWhiteSpace(this String value)
    {
        return String.IsNullOrWhiteSpace(value);
    }
}