diff --git a/src/main/java/cactusServer/resources/PlayersRest.java b/src/main/java/cactusServer/resources/PlayersRest.java
index 6820d4f..a9aefc6 100644
--- a/src/main/java/cactusServer/resources/PlayersRest.java
+++ b/src/main/java/cactusServer/resources/PlayersRest.java
@@ -11,6 +11,7 @@
 import javax.ws.rs.PathParam;
 import javax.ws.rs.Produces;
 import javax.ws.rs.QueryParam;
+import javax.ws.rs.WebApplicationException;
 import javax.ws.rs.core.MediaType;
 
 import org.ntlab.radishforandroidstudio.framework.model3D.Position3D;
@@ -66,7 +67,10 @@
 			@FormParam("animationClassToStart") EmoteState.EmoteType animationClassToStart) {
 		Player player = Instances.getInstance().updatePlayer(playerId, characterID, position, angle, cameraState,
 				animationClassToStart);
-		return JSON.encode(player);
+		if (player != null) {
+			return JSON.encode(player);
+		}
+		throw new WebApplicationException(400);
 	}
 	
 	@Path("/{playerId}")