"plugin" is being returned as null

I think the issue is that I am referencing plugin incorrectly. To explain what I mean by plugin, here is an example of what I am trying to reference externally. I have tried to debug this myself but I am stumped, it's probably something obvious but I just need another pair of eyes. Thank you heaps in advanced.

Code:

getServer().getPluginManager().registerEvents(new EventThing(), >> this <<) // where "this" is the plugin.

Here is a overview of the file structure related to this post.

src/main/java/me/mavendisrrpt/
-> App.java (main)

-> Listeners
--->BlockRegen.java

-> Tasks
--->RegenerateBlockTask.java

Quick context of the project: when mine ore, ore change to bedrock, then after 5 seconds it changes back to the original ore.

Here is the Listener for when the block is broken.

Code:

import me.mavendisrrpt.App; // main file
import me.mavendisrrpt.Tasks.RegenerateBlockTask;

import a.bunch.of.bukkit.stuff

public final class BlockBreakListener implements Listener {

    App plugin;

    @EventHandler
    public void onBlockBreak(BlockBreakEvent event) {
        this.plugin = plugin;
        Player player = event.getPlayer();
        Block block = event.getBlock();
        Material blockType = block.getType();

        switch (blockType) {
            case IRON_ORE:
                block.setType(Material.BEDROCK);
                player.getInventory().addItem(new ItemStack(Material.IRON_ORE, 1));
                event.setCancelled(true);
                System.out.println(plugin); // returning NULL
                // BukkitTask task = new RegenerateBlockTask(plugin, block).runTaskLater(plugin, 100L);
                break;
       
            default:
                break;
        }

    }

}

Here is the main file

Code:

package me.mavendisrrpt;

import org.bukkit.plugin.java.JavaPlugin;

import me.mavendisrrpt.Commands.TestCommand;
import me.mavendisrrpt.Listeners.BlockRegen;


public class App extends JavaPlugin {
    @Override
    public void onEnable() {
        getCommand("test").setExecutor(new TestCommand());
        getServer().getPluginManager().registerEvents(new BlockBreakListener(), this);
    }
    @Override
    public void onDisable() {
        // potatoes are tasty
    }
}