if(ctx.field_name != null){
  ArrayList lower_array = new ArrayList();
  for (item in ctx.field_name){
    ArrayList temp = new ArrayList();
    for(map_entry in item.entrySet()){
      temp.add([map_entry.getKey().toLowerCase():map_entry.getValue()])
    }
    lower_array.add(temp);
  }
  ctx.field_name = lower_array;
}