Fixed errors when disabling the plugin due to running new tasks (#100)

src/main/java/com/bgsoftware/wildloaders/WildLoadersPlugin.java

@@ -18,6 +18,7 @@ import com.bgsoftware.wildloaders.listeners.BlocksListener;
 import com.bgsoftware.wildloaders.listeners.ChunksListener;
 import com.bgsoftware.wildloaders.listeners.PlayersListener;
 import com.bgsoftware.wildloaders.nms.NMSAdapter;
+import com.bgsoftware.wildloaders.scheduler.Scheduler;
 import com.bgsoftware.wildloaders.utils.database.Database;
 import org.bstats.bukkit.Metrics;
 import org.bukkit.Bukkit;
@@ -44,6 +45,7 @@ public final class WildLoadersPlugin extends JavaPlugin implements WildLoaders {
     @Override
     public void onLoad() {
         plugin = this;
+        Scheduler.initialize();
 
         DependenciesManager.inject(this);
 
@@ -93,11 +95,13 @@ public final class WildLoadersPlugin extends JavaPlugin implements WildLoaders {
 
     @Override
     public void onDisable() {
-        if (shouldEnable) {
-            Database.stop();
-            loadersHandler.removeChunkLoaders();
-            npcHandler.killAllNPCs();
-        }
+        if (!shouldEnable)
+            return;
+
+        Scheduler.disable();
+        Database.stop();
+        loadersHandler.removeChunkLoaders();
+        npcHandler.killAllNPCs();
     }
 
     private boolean loadNMSAdapter() {

src/main/java/com/bgsoftware/wildloaders/scheduler/Scheduler.java

@@ -6,6 +6,9 @@ import org.bukkit.World;
 import org.bukkit.entity.Entity;
 
 public class Scheduler {
+
+    private static final ScheduledTask NULL_TASK = () -> {};
+
     private static final ISchedulerImplementation IMP = initializeSchedulerImplementation();
 
     private static ISchedulerImplementation initializeSchedulerImplementation() {
@@ -24,6 +27,8 @@ public class Scheduler {
         }
     }
 
+    private static boolean isEnabled = true;
+
     private Scheduler() {
 
     }
@@ -32,23 +37,43 @@ public class Scheduler {
         // Do nothing, load static initializer
     }
 
+    public static void disable() {
+        isEnabled = false;
+    }
+
     public static boolean isRegionScheduler() {
         return IMP.isRegionScheduler();
     }
 
     public static ScheduledTask runTask(World world, int chunkX, int chunkZ, Runnable task, long delay) {
+        if (!isEnabled) {
+            return executeNow(task);
+        }
+
         return IMP.scheduleTask(world, chunkX, chunkZ, task, delay);
     }
 
     public static ScheduledTask runTask(Entity entity, Runnable task, long delay) {
+        if (!isEnabled) {
+            return executeNow(task);
+        }
+
         return IMP.scheduleTask(entity, task, delay);
     }
 
     public static ScheduledTask runTask(Runnable task, long delay) {
+        if (!isEnabled) {
+            return executeNow(task);
+        }
+
         return IMP.scheduleTask(task, delay);
     }
 
     public static ScheduledTask runTaskAsync(Runnable task, long delay) {
+        if (!isEnabled) {
+            return executeNow(task);
+        }
+
         return IMP.scheduleAsyncTask(task, delay);
     }
 
@@ -84,4 +109,9 @@ public class Scheduler {
         return runTaskAsync(task, 0L);
     }
 
+    private static ScheduledTask executeNow(Runnable task) {
+        task.run();
+        return NULL_TASK;
+    }
+
 }