Variable is nothing at first time page load. Why?

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C#

VB

WPF

Guys,

I'm creating a WPF page which to show current map location of the device at default page. What I'm weird is, my application log has captured a variable passed to the function is NOTHING where before it go into the function, the variable "devloc" with be hold a value from configuration settings let's say GF or LG from udt.devfloor.

It appear when I'm breakpoint to the udt.devfloor, it will skip it value to devloc and jump to the exception directly. If I continue run after it breakpoint, it will like cycle loop the instance back and the cycle is ok.

The exception:-

{"Object reference not set to an instance of an object."}

Find my flow below:-

Public Sub New()
        MyBase.New()
        Me.InitializeComponent()
        devloc= udt_config.devfloor
        ViewSelectedDeviceLoc(devloc, 100)
End Sub
Private Sub ViewSelectedDeviceLoc(ByVal floor As String, ByVal width As Integer)
    Try
        If floor.Contains("C/") Then '// this is where the floor become nothing
            img_maps.Source = obj_core.ReturnSpecificImage(mymapspath & "B1.png", width)
        Else
            img_maps.Source = obj_core.ReturnSpecificImage(mymapspath & floor & ".png", width)
        End If
        img_maps.Stretch = Stretch.Uniform
        img_maps.StretchDirection = StretchDirection.Both
    Catch ex As Exception
        strMsg = "[" & strlogpage & "] Error at view " & floor & " map 2. Ex:" & ex.Message '//exception direct here
        App.LogEvents(strMsg, EventLogEntryType.Error)
    End Try
End Sub

What I have tried:

Trying to reinitialize the variable if it nothing:-

If IsNothing(udt_config.devfloor) Then
devloc= udt_config.devfloor
End If

It still same. It just happen at the very first time when application is started and the page is load for the very first time. It will not having