Some .net/mono frameworks do not support the IsNullOrWhiteSpace method. The code below provides a simple replacement.

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

    var index = 0;
    while (index < value.Length)
    {
        if (char.IsWhiteSpace(value[index]))
        {
            index++;
        }
        else
        {
            return false;
        }
    }

    return true;
}