docs: def to_dictionary(
              self,
              key_selector=None,
              value_selector=None):
          """Build a dictionary from the source sequence.
  
          Args:
              key_selector: A unary callable to extract a key from each item or None.
                  If None, the default key selector produces a single dictionary key, which
                  if the key of this Grouping.
  
              value_selector: A unary callable to extract a value from each item.
                  If None, the default value selector produces a list, which contains all
                  elements from this Grouping.
  
          Note: This method uses immediate execution.
  
          Raises:
              ValueError: If the Queryable is closed.
              TypeError: If key_selector is not callable.
              TypeError: If value_selector is not callable.
          """
          if key_selector is None:
              key_selector = lambda _: self.key
  
          if value_selector is None:
              value_selector = lambda _: self.to_list()
  
          return super(Grouping, self).to_dictionary(key_selector, value_selector)