def parse_header(line)
      return if IOStreams.blank?(line) || !parser.requires_header?

      header.columns = parser.parse(line)
    end
def parse_header(line)
      return if IOStreams.blank?(line) || !parser.requires_header?

      header.columns = parser.parse(line)
    end
Returns [Array] the header row/line after parsing and cleansing.
 Returns `nil` if the row/line is blank, or a header is not required for the supplied format (:json, :hash).

 Notes:
 * Call `header?` first to determine if the header should be parsed first.
 * The header columns are set after parsing the row, but the header is not cleansed.