[Bug] A custom responder return with an empty error

Describe the bug
I have written a bare minimal responder that just returns a success message for a request from TheHive. However, I get the status failure without much information.

#!/usr/bin/env python3

from cortexutils.responder import Responder

class SampleService(Responder):
    def __init__(self):
        Responder.__init__(self)

    def run(self):
        Responder.run(self)
        self.report({'message': "success"})

    def operations(self, raw):
        return [self.build_operation("AddTagToCase", tag="sampleId:id-1")]

if __name__ == "__main__":
    SampleService().run()

When I run the responder from TheHive, I get the below output in the application logs with a warning saying
[warn] o.t.c.s.DockerJobRunnerSrv - The worker didn't generate output file.

[info] o.t.c.s.DockerJobRunnerSrv - Execute container bf99c645848c9ca0f9f00d573b7f1b8d21220f272f9003b4fb44b8c87c0370b9
  timeout: 30 minutes
  image  : cortex-neurons/sample_service:0.2
  volume : /tmp/cortex-jobs/cortex-job-Fk2v5ocBSFpERmG9YbQq-7518629213985387577:/job
[info] c.s.d.c.DefaultDockerClient - Starting container with Id: bf99c645848c9ca0f9f00d573b7f1b8d21220f272f9003b4fb44b8c87c0370b9
[info] o.t.c.s.AccessLogFilter - 192.168.65.205 GET /api/alert took 17ms and returned 200 2 bytes
[warn] o.t.c.s.DockerJobRunnerSrv - The worker didn't generate output file.
[info] o.t.c.s.JobSrv - Job Fk2v5ocBSFpERmG9YbQq has finished with status Failure
[info] o.t.c.s.AuditActor - Job Fk2v5ocBSFpERmG9YbQq has be updated (JsDefined("Failure"))

In cortex UI I can see the observable information as input and output(Report) only contains,

{
  "errorMessage": "",
  "input": null,
  "success": false
}

Work environment

• Cortex version: thehiveproject/cortex:3.1.7-withdeps
• TheHive version: strangebee/thehive:5.1
• Elasticsearch version: docker.elastic.co/elasticsearch/elasticsearch:7.17.9
• Cassandra version: cassandra:4

Additional information

• I have setup services based on information provided at https://docs.strangebee.com/thehive/setup/installation/docker/#using-your-own-configuration-file
• I can successfully run MISP Analyser without any issues and get the correct output in TheHive
• I have been pulling my hair for hours

Start with the custom responder entry points shown in the report: cortexutils.responder.Responder.run, operations, and report. Reproduce the responder from the issue and compare its behavior with the working MISP Analyser; done means the responder generates the expected output file and the Cortex report no longer shows an empty errorMessage.