Added check for sign validity. Fixed #379

src/main/java/myessentials/entities/sign/Sign.java

@@ -1,5 +1,6 @@
 package myessentials.entities.sign;
 
+import myessentials.MyEssentialsCore;
 import myessentials.entities.BlockPos;
 import net.minecraft.entity.player.EntityPlayer;
 import net.minecraft.init.Blocks;
@@ -28,6 +29,8 @@ public abstract class Sign {
 
     protected abstract String[] getText();
 
+    protected abstract boolean isValid();
+
     public void onShiftRightClick(EntityPlayer player) {
     }
 
@@ -75,6 +78,16 @@ public void deleteSignBlock() {
     }
 
     public static class Container extends ArrayList<Sign> {
+        @Override
+        public boolean add(Sign sign) {
+            if(sign.isValid()) {
+                return super.add(sign);
+            } else {
+                MyEssentialsCore.instance.LOG.error("Failed to validate a special sign at location ({}, {}, {}; DIM: {})", sign.bp.getX(), sign.bp.getY(), sign.bp.getZ(), sign.bp.getDim());
+                return false;
+            }
+        }
+
         public Sign get(BlockPos bp) {
             for(Sign sign : this) {
                 if(bp.equals(sign.bp)) {