--- ../work/decompile-bb26c12b/net/minecraft/server/TileEntityPiston.java	2014-11-27 08:59:46.917420896 +1100
+++ src/main/java/net/minecraft/server/TileEntityPiston.java	2014-11-27 08:42:10.152850911 +1100
@@ -104,6 +104,7 @@
     }
 
     public void c() {
+        if (this.world == null) return; // CraftBukkit
         this.j = this.i;
         if (this.j >= 1.0F) {
             this.a(1.0F, 0.25F);