code: def license(self, key, value):
      
      def _get_license(value):
          a_values = force_list(value.get('a'))
  
          oa_licenses = [el for el in a_values if el == 'OA' or el == 'Open Access']
          other_licenses = [el for el in a_values if el != 'OA' and el != 'Open Access']
  
          if not other_licenses:
              return force_single_element(oa_licenses)
          return force_single_element(other_licenses)
  
      def _get_material(value):
          material = value.get('3', '').lower()
          if material == 'article':
              return 'publication'
          return material
  
      return {
          'imposing': value.get('b'),
          'license': _get_license(value),
          'material': _get_material(value),
          'url': value.get('u'),
      }
docs: Populate the ``license`` key.