--- a/net/minecraft/world/gen/feature/structure/StructurePiece.java
+++ b/net/minecraft/world/gen/feature/structure/StructurePiece.java
@@ -48,6 +48,9 @@
    }
 
    public final NBTTagCompound func_143010_b() {
+      if (StructureIO.func_143036_a(this) == null) { // FORGE: Friendlier error then the Null String error below.
+         throw new RuntimeException("StructureComponent \"" + this.getClass().getName() + "\" missing ID Mapping, Modder see MapGenStructureIO");
+      }
       NBTTagCompound nbttagcompound = new NBTTagCompound();
       nbttagcompound.func_74778_a("id", StructureIO.func_143036_a(this));
       nbttagcompound.func_74782_a("BB", this.field_74887_e.func_151535_h());