Added Hook#getFailureCause() and fixed NPE in HooksManager

src/main/java/world/bentobox/bentobox/api/hooks/Hook.java

@@ -47,4 +47,10 @@ public abstract class Hook {
      * @return true if it successfully hooked into the plugin, false otherwise.
      */
     public abstract boolean hook();
+
+    /**
+     * Returns an explanation that will be sent to the user to tell them why the hook process did not succeed.
+     * @return the probable causes why the hook process did not succeed.
+     */
+    public abstract String getFailureCause();
 }

src/main/java/world/bentobox/bentobox/managers/HooksManager.java

@@ -3,6 +3,7 @@ package world.bentobox.bentobox.managers;
 import world.bentobox.bentobox.BentoBox;
 import world.bentobox.bentobox.api.hooks.Hook;
 
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
 
@@ -16,6 +17,7 @@ public class HooksManager {
 
     public HooksManager(BentoBox plugin) {
         this.plugin = plugin;
+        this.hooks = new ArrayList<>();
     }
 
     public void registerHook(Hook hook) {
@@ -24,7 +26,7 @@ public class HooksManager {
             if (hook.hook()) {
                 hooks.add(hook);
             } else {
-                plugin.log("Could not hook with " + hook.getPluginName() + ". Skipping...");
+                plugin.log("Could not hook with " + hook.getPluginName() + " because: " + hook.getFailureCause() + ". Skipping...");
             }
         }
     }