def enrich_value(value)
      set_label(value) if value.is_a?(DPLA::MAP::TimeSpan) && 
                          value.prefLabel.empty?
      value
    end
def enrich_value(value)
      set_label(value) if value.is_a?(DPLA::MAP::TimeSpan) && 
                          value.prefLabel.empty?
      value
    end
Add a prefLabel for `DPLA::MAP::TimeSpan` objects with begin/end dates

 @param value [DPLA::MAP::TimeSpan, String, Object]

 @return [DPLA::MAP::TimeSpan, Object] a new `TimeSpan` object containing
   the generated prefLabel