B4J Question Why do I need this line?

TR.Initialize(File.OpenInput(f,""))
Do While line <> Null
line = TR.ReadLine
If line = Null Then Exit
WriteTextArea
Loop
TR.Close
End Sub

Sub WriteTextArea

It looks totally redundant to me but without it the Do While loop try's to take too many lines and I get this error: java.lang.NullPointerException