docs: def serialize_to_headers(self):
          """Serialize to a dict of HTTP headers.
  
          Used in responses to HTTP HEAD requests. As with regular HTTP GET requests, HEAD
          requests may return DataONE Exceptions. Since a response to a HEAD request
          cannot include a body, the error is returned as a set of HTTP headers instead of
          an XML document.
  
          """
          return {
              'DataONE-Exception-Name': self.__class__.__name__,
              'DataONE-Exception-ErrorCode': self._format_header(self.errorCode),
              'DataONE-Exception-DetailCode': self._format_header(self.detailCode),
              'DataONE-Exception-Description': self._format_header(self.description),
              'DataONE-Exception-TraceInformation': self._format_header(
                  self.traceInformation
              ),
              'DataONE-Exception-Identifier': self._format_header(self.identifier),
              'DataONE-Exception-NodeID': self._format_header(self.nodeId),
          }