code: def set_list_predicates(self):
          
          results = self.rml.query("""
                  SELECT DISTINCT ?subj_class ?list_field
                  {
                      ?bn rr:datatype rdf:List .
                      ?bn rr:predicate ?list_field .
                      ?s ?p ?bn .
                      ?s rr:subjectMap ?sm_bn .
                      ?sm_bn rr:class ?subj_class .
                  }""")
          list_preds = [(Uri(row[0]).sparql, Uri(row[1]).sparql)
                        for row in results]
          array_fields = {}
          for tup in list_preds:
              try:
                  array_fields[tup[0]].append(tup[1])
              except KeyError:
                  array_fields[tup[0]] = [tup[1]]
          self.array_fields = array_fields
docs: Reads through the rml mappings and determines all fields that should
          map to a list/array with a json output