NPE fix in redstone

src/main/java/net/minecraft/server/BlockRedstoneWire.java

@@ -280,7 +280,7 @@ public class BlockRedstoneWire extends Block {
             if (!flag) {
                 this.b_(world, i, j, k, i1);
                 world.e(i, j, k, 0);
-            } else if(Block.byId[l].c() || Block.DIODE_OFF.id == l && Block.DIODE_ON.id == l) { //condition added by Craftbukkit
+            } else if((Block.byId[l] != null && Block.byId[l].c()) || Block.DIODE_OFF.id == l && Block.DIODE_ON.id == l) { //condition added by Craftbukkit
                 this.g(world, i, j, k);
             }