Fixes errors when loading greenhouses.

src/main/java/world/bentobox/greenhouses/managers/GreenhouseManager.java

@@ -5,6 +5,7 @@ import java.util.List;
 import java.util.Set;
 
 import org.bukkit.Location;
+import org.bukkit.block.Biome;
 import org.bukkit.event.EventHandler;
 import org.bukkit.event.Listener;
 
@@ -47,7 +48,8 @@ public class GreenhouseManager implements Listener {
         NULL,
         SUCCESS,
         FAIL_NO_RECIPE_FOUND,
-        FAIL_INSUFFICIENT_BLOCKS
+        FAIL_INSUFFICIENT_BLOCKS,
+        FAIL_NO_WORLD, FAIL_UNKNOWN_RECIPE
     }
 
     private final Greenhouses addon;
@@ -94,12 +96,21 @@ public class GreenhouseManager implements Listener {
                 toBeRemoved.add(g);
                 break;
             case FAIL_OVERLAPPING:
+                addon.logError("Greenhouse overlaps with another greenhouse. Skipping...");
+                break;
             case NULL:
-                addon.logError(result.name());
+                addon.logError("Null location of greenhouse. Cannot load. Skipping...");
                 break;
             case SUCCESS:
                 activateGreenhouse(g);
                 break;
+            case FAIL_NO_WORLD:
+                addon.logError("Database contains greenhouse for a non-loaded world. Skipping...");
+                break;
+            case FAIL_UNKNOWN_RECIPE:
+                addon.logError("Greenhouse uses a recipe that does not exist in the biomes.yml. Skipping...");
+                addon.logError("Greenhouse Id " + g.getUniqueId());
+                break;
             default:
                 break;
 
@@ -178,10 +189,15 @@ public class GreenhouseManager implements Listener {
     }
 
     private void activateGreenhouse(Greenhouse gh) {
+        Biome ghBiome = gh.getBiomeRecipe().getBiome();
+        if (ghBiome == null) {
+            addon.logError("Biome recipe error - no such biome for " + gh.getBiomeRecipe().getName());
+            return;
+        }
         for (int x = (int)gh.getBoundingBox().getMinX(); x < gh.getBoundingBox().getMaxX(); x+=4) {
             for (int z = (int)gh.getBoundingBox().getMinZ(); z < gh.getBoundingBox().getMaxZ(); z+=4) {
                 for (int y = (int)gh.getBoundingBox().getMinY(); y < gh.getBoundingBox().getMaxY(); y+=4) {
-                    gh.getWorld().setBiome(x, y, z, gh.getBiomeRecipe().getBiome());
+                    gh.getWorld().setBiome(x, y, z, ghBiome);
                 }
             }
         }

src/main/java/world/bentobox/greenhouses/managers/GreenhouseMap.java

@@ -33,6 +33,13 @@ public class GreenhouseMap {
      * @return result {@link GreenhouseResult}
      */
     public GreenhouseResult addGreenhouse(Greenhouse greenhouse) {
+        // Validation checks
+        if (greenhouse.getBiomeRecipe() == null) {
+            return GreenhouseResult.FAIL_UNKNOWN_RECIPE;
+        }
+        if (greenhouse.getWorld() == null) {
+            return GreenhouseResult.FAIL_NO_WORLD;
+        }
         if (greenhouse.getLocation() == null) {
             return GreenhouseResult.NULL;
         }