when initially creating the string, try this...
VB Code:
  1. [Color=Blue]string[/color] MyString = [Color=Blue]string[/color].Empty;
then you can check if the string is empty or not like this....
VB Code:
  1. [Color=Blue]private[/color] [Color=Blue]void[/color] button1_Click([Color=Blue]object[/color] sender, System.EventArgs e)
  2.         {
  3.             [Color=Blue]string[/color] MyString = [Color=Blue]string[/color].Empty;
  4.             [Color=Blue]if[/color](MyString==[Color=Blue]string[/color].Empty)
  5.             {
  6.                  MessageBox.Show("it's empty");
  7.             }
  8.             [Color=Blue]else
  9. [/color]           {
  10.                  MessageBox.Show("it's NOT empty");
  11.             }
  12.         }