Finish Old Spigot Partial Fix (https://github.com/PaperSpigot/Paper-1.7/blob/master/CraftBukkit-Patches/0019-Prevent-NPE-in-CraftSign.patch)

src/main/java/org/bukkit/craftbukkit/block/CraftSign.java

@@ -40,7 +40,7 @@ public class CraftSign extends CraftBlockState implements Sign {
     public boolean update(boolean force, boolean applyPhysics) {
         boolean result = super.update(force, applyPhysics);
 
-        if (result) {
+        if (result && sign != null) {
             sign.signText = sanitizeLines(lines);
             sign.markDirty();
         }