Null check always returns null, if removed returns Object reference not set to an instance of an object.

Question

I have some code which gets child items for a menu via the GetChildren function which takes a list of menuData:

Dim builtMenu As New List(Of MenuData)(_rawData.FindAll(Function(item) item.GroupingID = 0))

For Each menuData As MenuData In builtMenu
             If menuData.Children IsNot Nothing Then
            menuData.Children.AddRange(GetChildren(menuData))
             End If
        Next

If I check if menudata.children isnot nothing, it always is nothing because the GetChildren function is yet to run (providing the child items, which do exist). If I remove this check and just have this code:

Dim builtMenu As New List(Of MenuData)(_rawData.FindAll(Function(item) item.GroupingID = 0))

For Each menuData As MenuData In builtMenu  
            menuData.Children.AddRange(GetChildren(menuData)) 
        Next

Then I am presented with a Object reference not set to an instance of an object error on menuData.Children.AddRange(GetChildren(menuData))

Please can you tell me how I get around this problem? Thanks a lot

Answer 1

Your menuData.Children has never been instantiated, so it is a null (Nothing) reference.

You need to instantiate it before you use it:

Dim builtMenu As New List(Of MenuData)(_rawData.FindAll(Function(item) item.GroupingID = 0))
menuData.Children = New List(Of MenuData)

For Each menuData As MenuData In builtMenu  
    menuData.Children.AddRange(GetChildren(menuData)) 
Next