docs: def dropna(self):
          """Returns MultiIndex without any rows containing null values according to Baloo's convention.
  
          Returns
          -------
          MultiIndex
              MultiIndex with no null values.
  
          """
          not_nas = [v.notna() for v in self.values]
          and_filter = reduce(lambda x, y: x & y, not_nas)
  
          return self[and_filter]