We should return "" not null for 'corrupt' signs.

CraftBukkit-Patches/0041-Prevent-NPE-in-CraftSign.patch

@@ -1,4 +1,4 @@
-From 289f93ad3e999628f5d13a5da0fa2939cccbb5dd Mon Sep 17 00:00:00 2001
+From 03f9257d5a0ba384c73251024050cebfe4fc348a Mon Sep 17 00:00:00 2001
 From: md_5 <md_5@live.com.au>
 Date: Mon, 18 Mar 2013 20:01:44 +1100
 Subject: [PATCH] Prevent NPE in CraftSign
@@ -9,7 +9,7 @@ This commit prevents the constructor of CraftSign throwing an NPE when it cannot
  1 file changed, 7 insertions(+), 1 deletion(-)
 
 diff --git a/src/main/java/org/bukkit/craftbukkit/block/CraftSign.java b/src/main/java/org/bukkit/craftbukkit/block/CraftSign.java
-index 8e8a1c5..8b7d226 100644
+index 8e8a1c5..87af049 100644
 --- a/src/main/java/org/bukkit/craftbukkit/block/CraftSign.java
 +++ b/src/main/java/org/bukkit/craftbukkit/block/CraftSign.java
 @@ -14,6 +14,12 @@ public class CraftSign extends CraftBlockState implements Sign {
@@ -18,7 +18,7 @@ index 8e8a1c5..8b7d226 100644
          sign = (TileEntitySign) world.getTileEntityAt(getX(), getY(), getZ());
 +        // Spigot start
 +        if (sign == null) {
-+            lines = new String[4];
++            lines = new String[]{"", "", "", ""};
 +            return;
 +        }
 +        // Spigot end