CatServer/patches/net/minecraft/world/gen/structure/StructureStart.java.patch

--- ../src-base/minecraft/net/minecraft/world/gen/structure/StructureStart.java
+++ ../src-work/minecraft/net/minecraft/world/gen/structure/StructureStart.java
@@ -63,6 +63,10 @@
 
     public NBTTagCompound writeStructureComponentsToNBT(int chunkX, int chunkZ)
     {
+        if (MapGenStructureIO.getStructureStartName(this) == null) // This is just a more friendly error instead of the 'Null String' below
+        {
+            throw new RuntimeException("StructureStart \"" + this.getClass().getName() + "\" missing ID Mapping, Modder see MapGenStructureIO");
+        }
         NBTTagCompound nbttagcompound = new NBTTagCompound();
         nbttagcompound.setString("id", MapGenStructureIO.getStructureStartName(this));
         nbttagcompound.setInteger("ChunkX", chunkX);
@@ -98,7 +102,8 @@
 
         for (int i = 0; i < nbttaglist.tagCount(); ++i)
         {
-            this.components.add(MapGenStructureIO.getStructureComponent(nbttaglist.getCompoundTagAt(i), worldIn));
+            StructureComponent tmp = MapGenStructureIO.getStructureComponent(nbttaglist.getCompoundTagAt(i), worldIn);
+            if (tmp != null) this.components.add(tmp); //Forge: Prevent NPEs further down the line when a componenet can't be loaded.
         }
 
         this.readFromNBT(tagCompound);