docs: def get_missing_value_key(d):
      """
      Get the Missing Value entry from a table of data. If none is found, try the columns.
      If still none found, prompt user.
  
      :param dict d: Table of data
      :return str _mv: Missing Value
      """
      _mv = "nan"
  
      # Attempt to find a table-level missing value key
      try:
          # check for missing value key at the table root
          _mv = d["missingValue"]
      except KeyError as e:
          logger_misc.info("get_missing_value: No missing value key found: {}".format(e))
      except AttributeError as e:
          logger_misc.warn("get_missing_value: Column is wrong data type: {}".format(e))
  
      # No table-level missing value found. Attempt to find a column-level missing value key
      if not _mv:
          try:
              # loop for each column of data, searching for a missing value key
              for k, v in d["columns"].items():
                  # found a column with a missing value key. Store it and exit the loop.
                  _mv = v["missingValue"]
                  break
          except KeyError:
              # There are no columns in this table. We've got bigger problems!
              pass
  
      # No table-level or column-level missing value. Out of places to look. Ask the user to enter the missing value
      # used in this data
      # if not _mv:
      #     print("No 'missingValue' key provided. Please type the missingValue used in this file: {}\n".format(filename))
      #     _mv = input("missingValue: ")
      return _mv