Bugfix in setparent.

src/engine/objects/Zone.java

@@ -253,7 +253,17 @@ public class Zone extends AbstractGameObject {
 
         this.setBounds();
 
-        if (this.getHeightMap() != null && this.getHeightMap().getSeaLevel() != 0)
+        if (this.getParent() == null) {
+            this.seaLevel = 0;
+            return;
+        }
+
+        if (this.getHeightMap() == null) {
+            this.seaLevel = this.parent.seaLevel;
+            return;
+        }
+
+        if (this.getHeightMap().getSeaLevel() != 0)
             this.seaLevel = this.worldAltitude + this.getHeightMap().getSeaLevel();
         else
             this.seaLevel = this.parent.seaLevel;