Use isEmpty.

Using Collection.size() to test for emptiness works, but using
Collection.isEmpty() makes the code more readable and can be more
performant. The time complexity of any isEmpty() method implementation
should be O(1) whereas some implementations of size() can be O(n).

In this case, it's not a big deal, just a code smell.

src/main/java/world/bentobox/border/Border.java

@@ -26,7 +26,7 @@ public final class Border extends Addon {
 
     private @NonNull List<GameModeAddon> gameModes = new ArrayList<>();
 
-    private final Set<BorderType> availableBorderTypes = EnumSet.of(BorderType.Barrier);
+    private final Set<BorderType> availableBorderTypes = EnumSet.of(BorderType.BARRIER);
 
     @Override
     public void onLoad() {
@@ -49,7 +49,7 @@ public void onEnable() {
                 this.setState(State.DISABLED);
                 return;
             }
-            availableBorderTypes.add(BorderType.Vanilla);
+            availableBorderTypes.add(BorderType.VANILLA);
         }
         gameModes.clear();
         // Register commands
@@ -64,7 +64,7 @@ public void onEnable() {
             }
         });
 
-        if (gameModes.size() > 0) {
+        if (!gameModes.isEmpty()) {
             borderShower = createBorder();
             registerListener(new PlayerListener(this));
         }
@@ -79,7 +79,7 @@ private BorderShower createBorder() {
         BorderShower customBorder = new ShowBarrier(this);
         BorderShower wbapiBorder = getSettings().isUseWbapi()
                 ? new ShowWorldBorder(this)
-                : null;
+                        : null;
         return new PerPlayerBorderProxy(this, customBorder, wbapiBorder);
     }