SyncVar hook value is null

 using UnityEngine;
 using System.Collections;
 using UnityEngine.Networking;
 
 public class PrefabScript : NetworkBehaviour {
 
     [SyncVar(hook="MakeTheChange")]
     public Material material; 
 
     [SyncVar]
     public Material newMaterial;
 
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 
     void MakeTheChange(Material value) {
         GetComponent<MeshRenderer> ().material = value;
     }
 }
 

I can see MakeTheChange firing in the debugger, but value is always null. Any idea why it isn't passing the correct value?