How To Avoid Storing Different Type Of Objects In The Same Place When Represent The Same But With A Different Data Structure

This is in my opinion an abstract problem and I hope I can explain it well. I happened to find the same kind of problem in a completely different project and now I have it again and I would like to avoid it if possible.

I'm creating some classes to simplify some tasks for some specific requirements we have in some projects at work.

I have a class that creates objects which maps the values from webcontrols to an object properties similar to this

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The problem I have it's sometimes I have to store a non container object in a place (in an object's attribute) and sometimes I have to a store a container object in the same place for storing the values of a webcontrol (a webcontrol can sometimes hold several values like a checkboxlist). I dont like this at all, because some time ago when working in a non commercial compiler, when parsing and generating the intermediate code I had sometimes to store a container in a place, and sometimes I had to store a non container in the same place, and having to ask in other parts of the code if what you are reading is this type of object, or this another type of object, it is something really annoying and it mess up the code. Is there any tips about what it would be better to do to avoid this kind of situations or nothing can be done to avoid it sometimes?