Why is my Android Java Object null when invoking a method?

I'm trying to come to terms with how an Android plugin in Unity works with a very simple plugin.

In Android Studio I made an Android Library with a single class in the following code.

 package com.example.mylibrary;
 
 public class Thing {
 
     public static Thing instance;
 
     Thing () {
         Thing.instance = this;
     }
 
     public String SayHi () {
         return "hi";
     }
 }

I couldn't figure out how to export a single thing to .jar or .aar, so I just did build -> build APK, and copied the mylibrary-debug.aar file from my export location into my Unity project.

Then in Unity I made a simple script that tried to invoke the SayHi Java method.

 using UnityEngine;
 
 public class DoTheThing : MonoBehaviour {
 
    void Start () {
       AndroidJavaClass _thing = new AndroidJavaClass("com.example.mylibrary.Thing");
       AndroidJavaObject thing = _thing.GetStatic<AndroidJavaObject>("instance");
       Debug.Log(thing.Call<string>("SayHi"));
    }
 }

When invoking this method, I get a Null Reference Exception, and I'm not sure why my Java code is failing. Is the constructor in the Java code never being called? That would be why instance is null.