code: def map_sites(self, stmts):
          valid_statements = []
          mapped_statements = []
          for stmt in stmts:
              mapped_stmt = self.map_stmt_sites(stmt)
              if mapped_stmt is not None:
                  mapped_statements.append(mapped_stmt)
              else:
                  valid_statements.append(stmt)
          return valid_statements, mapped_statements