docs: def dropna(self, subset=None):
          """Remove missing values according to Baloo's convention.
  
          Parameters
          ----------
          subset : list of str, optional
              Which columns to check for missing values in.
  
          Returns
          -------
          DataFrame
              DataFrame with no null values in columns.
  
          """
          subset = check_and_obtain_subset_columns(subset, self)
          not_nas = [v.notna() for v in self[subset]._iter()]
          and_filter = reduce(lambda x, y: x & y, not_nas)
  
          return self[and_filter]