C# - Retrieve Internal Member Of Nested Class By Reflection

I know that the MenuItem class contains an internal class named MenuItemData, which contains itself an internal member named onDrawItem. Given a MenuItem, I want to retrieve the object corresponding to the member onDrawItem. But all I manage to do is to get the FieldInfo, not the object itself.

Here is my code:
Dim obj As Object
Dim fi As FieldInfo
Dim item as System.Windows.Forms.MenuItem
Dim mType As System.Type
[Code] .....

When reaching the last line, I get an error saying something like that (it's traduced):
The field 'onDrawItem' défined in type 'System.Windows.Forms.MenuItem+MenuItemData' is not a field of the target object of type 'System.Windows.Forms.MenuItem. I don't know what object to pass to the GetValue function on the last line. My goal is to remove the base eventHandler of the menuItem, named DrawItem. See this post and the function RemoveClickEventin the accepted answer for a better understanding.