NullReferenceException on custom Class with Dictionary

I have a simple question today about some custom Classes that are not working as desired. For context, this is C# code in Xamarin Forms, building for UWP.

In my C# code, I have two custom classes. We will call them Smaller and Bigger. Smaller is a simple class that only has a few instance variables. My issue is with the Bigger class, which includes a dictionary mapping strings to instances of my Smaller class. When I try to create an Indexer for the Bigger class, I want it to index into the dictionary included in the class.

Here is the code with relevant parts:

public class Smaller {
    ... // a bunch of instance variables, all strings, public and private versions.
}

public class Bigger {
    ...
    // other instance variables here...
    ...
    // the dictionary in question, mapping to Smaller instances
    private Dictionary<string, Smaller> _Info;
    public Dictionary<string, Smaller> Info {
        get => _Info;
        set { 
            _Info = value;
            OnPropertyChanged("Info");
        }
    }

    public Smaller this[string key] { // Indexer for Bigger class
        get => _Info[key];
        set => Info.Add(key, value);
    }
}

It is in the Indexer that I get my error, the NullReferenceException on my getter and setter. What is going wrong here? I have tried for both the getter and setter using the private _Info or public Info and neither one works for either.

The OnPropertyChanged don’t affect anything since I have other variables using them which work fine. Should I just get rid of having two variables, private and public? I am just doing that since the code is adapted from a template that uses the private and public instances.

Thanks!

>Solution :

this is null

private Dictionary<string, Smaller> _Info;

you need to initialize it

private Dictionary<string, Smaller> _Info = new Dictionary<string, Smaller>();