code: def unflatten(flat_dict: Dict[str, Any]) -> Dict[str, Any]:
      
      unflat: Dict[str, Any] = {}
  
      for compound_key, value in flat_dict.items():
          curr_dict = unflat
          parts = compound_key.split(".")
          for key in parts[:-1]:
              curr_value = curr_dict.get(key)
              if key not in curr_dict:
                  curr_dict[key] = {}
                  curr_dict = curr_dict[key]
              elif isinstance(curr_value, dict):
                  curr_dict = curr_value
              else:
                  raise ConfigurationError("flattened dictionary is invalid")
          if not isinstance(curr_dict, dict) or parts[-1] in curr_dict:
              raise ConfigurationError("flattened dictionary is invalid")
          else:
              curr_dict[parts[-1]] = value
  
      return unflat
docs: Given a "flattened" dict with compound keys, e.g.
          {"a.b": 0}
      unflatten it:
          {"a": {"b": 0}}