old_contents: from ..constants import FORMAT_CHECKS
  from ..post import HEADER_OPTIONAL_FIELD_TYPES, HEADER_REQUIRED_FIELD_TYPES
  from ..postprocessor import KnowledgePostProcessor
  
  
  class FormatChecks(KnowledgePostProcessor):
      _registry_keys = [FORMAT_CHECKS]
  
      def process(self, kp):
          headers = kp.headers
          for field, typ, _ in HEADER_REQUIRED_FIELD_TYPES:
              assert field in headers, \
                  "Required field `{field}` missing from headers."
          for field, typ, _ in \
                  HEADER_REQUIRED_FIELD_TYPES + HEADER_OPTIONAL_FIELD_TYPES:
              if field in headers:
                  header_field = headers[field]
                  assert isinstance(header_field, typ), \
                      f"Value for field `{field}` is of type " + \
                      f"{type(header_field)}, and needs to be of type {typ}."
  
new_contents: from ..constants import FORMAT_CHECKS
  from ..post import HEADER_OPTIONAL_FIELD_TYPES, HEADER_REQUIRED_FIELD_TYPES
  from ..postprocessor import KnowledgePostProcessor
  
  
  class FormatChecks(KnowledgePostProcessor):
      _registry_keys = [FORMAT_CHECKS]
  
      def process(self, kp):
          headers = kp.headers
          for field, typ, input in HEADER_REQUIRED_FIELD_TYPES:
              assert field in headers, "Required field `{}` missing from headers.".format(
                  field)
              assert isinstance(headers[field], typ), "Value for field `{}` is of type {}, and needs to be of type {}.".format(
                  field, type(headers[field]), typ)
          for field, typ, input in HEADER_OPTIONAL_FIELD_TYPES:
              if field in headers:
                  assert isinstance(headers[field], typ), "Value for field `{}` is of type {}, and needs to be of type {}.".format(
                      field, type(headers[field]), typ)
  
subject: Revert the latest changes due to CI build failure