Handle nulls if they happen

src/main/java/world/bentobox/bentobox/managers/island/IslandCache.java

@@ -538,7 +538,9 @@ public class IslandCache {
      * @return list of islands
      */
     public @NonNull List<Island> getIslands(UUID uniqueId) {
-        return islandsByUUID.getOrDefault(uniqueId, Collections.emptySet()).stream().map(this::getIslandById).toList();
+        return islandsByUUID.getOrDefault(uniqueId, Collections.emptySet()).stream().map(this::getIslandById)
+                .filter(Objects::nonNull) // Filter out null values
+                .toList();
     }
 
     /**

src/test/java/world/bentobox/bentobox/managers/island/IslandCacheTest.java

@@ -470,6 +470,23 @@ public class IslandCacheTest extends AbstractCommonSetup {
         assertTrue(ic.getIslands(owner).isEmpty());
     }
 
+    /**
+     * Test method for {@link world.bentobox.bentobox.managers.island.IslandCache#getIslands(java.util.UUID)}.
+     * @throws IntrospectionException 
+     * @throws NoSuchMethodException 
+     * @throws ClassNotFoundException 
+     * @throws InvocationTargetException 
+     * @throws IllegalAccessException 
+     * @throws InstantiationException 
+     */
+    @Test
+    public void testGetIslandsUUIDNoIslands() throws InstantiationException, IllegalAccessException,
+            InvocationTargetException, ClassNotFoundException, NoSuchMethodException, IntrospectionException {
+        // Test is WIP.
+        when(handler.loadObject(anyString())).thenReturn(null);
+        assertTrue(ic.getIslands(owner).isEmpty());
+    }
+
     /**
      * Test method for {@link world.bentobox.bentobox.managers.island.IslandCache#addIsland(world.bentobox.bentobox.database.objects.Island)}.
      */