code: def find_filled_col(self, col_list):
          
          for col in col_list:
              if col in self.df.columns:
                  if not all([is_null(val, False) for val in self.df[col]]):
                      return col
docs: return the first col_name from the list that is both
          a. present in self.df.columns and
          b. self.df[col_name] has at least one non-null value
  
          Parameters
          ----------
          self: MagicDataFrame
          col_list : iterable
             list of columns to check
  
          Returns
          ----------
          col_name : str