More tweaks

src/Physics/babylon.physicsHelper.ts

@@ -197,8 +197,12 @@ module BABYLON {
             if (!this._intersectsWithSphere(impostor, origin, radius)) {
                 return null;
             }
+            
+            if (impostor.object.getClassName() !== 'Mesh') {
+                return null;
+            }
 
-            var impostorObject = (<Mesh>impostor.object);
+            var impostorObject = <Mesh>impostor.object;
             var impostorObjectCenter = impostor.getObjectCenter();
             var direction = impostorObjectCenter.subtract(origin);
 
@@ -549,6 +553,10 @@ module BABYLON {
             if (!this._intersectsWithCylinder(impostor)) {
                 return null;
             }
+            
+            if (impostor.object.getClassName() !== 'Mesh') {
+                return null;
+            }
 
             var impostorObject = <Mesh>impostor.object;
             var impostorObjectCenter = impostor.getObjectCenter();

src/Physics/babylon.physicsImpostor.ts

@@ -27,6 +27,7 @@ module BABYLON {
         rotate(axis: Vector3, amount: number, space?: Space): TransformNode;
         translate(axis: Vector3, distance: number, space?: Space): TransformNode;
         setAbsolutePosition(absolutePosition: Vector3): TransformNode;
+        getClassName(): string;
     }
 
     export class PhysicsImpostor {