Object reference not set to an instance of an object? VB.NET

Question

I have this code here:

Dim MasterIndex As String()()

Private Function Lookup(ByVal Search_path As String) As Integer
    Dim i As Integer = 0
    Do Until MasterIndex(i)(0) Is Nothing
        If Search_path = MasterIndex(i)(0) Then
            Return MasterIndex(i)(1)
        End If
    Loop
    Return -1
End Function

Which gives me the error Object reference not set to an instance of an object occuring on the Do Until line. Why is this? How can I fix this?

Answer 1

The MasterIndex variable is never assigned that is why you have the exception

You should instantiate MasterIndex first by calling the New() constructor:

 Dim MasterIndex As new String()()

and fill it with data before calling the Lookup function.

Something like:

 Private MasterIndex As String()() = New String()() {New String() {"A1", "A2"}, New String() {"B1", "B2"}}

Answer 2

Either MasterIndex is not initialized or MasterIndex(0) is not initialized.

Can you show the code that initializes that variable, assuming you do that somewhere else in the program?

What happens if you put a breakpoint on that line and examine MasterIndex?