diff --git a/src/jrummikub/model/StoneTray.java b/src/jrummikub/model/StoneTray.java
index f215164..176c5f0 100644
--- a/src/jrummikub/model/StoneTray.java
+++ b/src/jrummikub/model/StoneTray.java
@@ -67,7 +67,9 @@ public class StoneTray<E extends Sizeable> implements
 	 *            {@link Position} to put the object
 	 */
 	public void drop(E object, Position position) {
-		drop(object, position, null);
+		if (object != null) {
+			drop(object, position, null);
+		}
 	}
 
 	@SuppressWarnings("unchecked")