String.IsNullOrBlank Extension Method

I know this is an old question but since it was bumped and it hasn't been mentioned already, as of .NET 4.0 you can simply use the String.IsNullOrWhiteSpace method to achieve the same result.

You could do:

public static bool IsNullOrBlank(this String text)
{
  return text==null || text.Trim().Length==0;
}

And then call it like this:

if(myString.IsNullOrBlank())
{
  throw new ArgumentException("Blank strings cannot be handled.");
}

This works because C# allows you to call extension method on null instances.