How does .NET Core DI determine unspecified generic parameter like ILogger?

(This question on ILogger is resolved in this question. My question asks how the DI system accomplishes it)

I was curious how .NET Core ILogger<MyClass> could be resolved for any type of MyClass. I checked the source code and found this one:

services.TryAdd(ServiceDescriptor.Singleton(typeof(ILogger<>), typeof(Logger<>)));

So I understand that, when I need ILogger<MyClass>, the DI will automatically create a Logger<MyClass>. My question is, from Reflection, how does it happen? I made this code to investigate:

        var t1 = typeof(IList<>);
        Console.WriteLine(t1.FullName); // System.Collections.Generic.IList`1
        Console.WriteLine(t1.IsGenericType); // True
        Console.WriteLine(t1.GetGenericArguments()[0].Name); // T
        Console.WriteLine(t1.GetGenericArguments()[0].FullName); // null

        var t2 = typeof(IList<int>);
        Console.WriteLine(t2.FullName); // System.Collections.Generic.IList`1...
        Console.WriteLine(t2.IsGenericType); // True
        Console.WriteLine(t2.GetGenericArguments()[0].Name); // Int32
        Console.WriteLine(t2.GetGenericArguments()[0].FullName); // System.Int32

Weirdly enough, t1 still has valid GetGenericArguments() result with the type being T (and null FullName). Is that how the DI implementation check if the input type is Something<>?