fix(workflow-engine): Prevent ValueError for missing ActionTarget in serializer

[sentry]

This PR addresses issue SENTRY-5QVV, where the WorkflowEngineActionSerializer would raise a ValueError: None is not a valid ActionTarget.

Problem:
The WorkflowEngineActionSerializer in src/sentry/incidents/endpoints/serializers/workflow_engine_action.py was attempting to instantiate the ActionTarget enum with None when an Action object's config dictionary was missing the target_type key. This scenario could occur for older Action records or specific action types (e.g., Sentry App actions) where target_type was not present in the config, leading to a ValueError during serialization, particularly when accessing endpoints like /api/0/organizations/{organization_id_or_slug}/combined-rules/.

Solution:

1. Null Guard: Modified the serialize method in WorkflowEngineActionSerializer to explicitly check if target_type is None before attempting to convert it to an ActionTarget enum member. If target_type is None, the serialized targetType field will now be None.
2. Type Annotation: Updated the type annotation for target_type from int to int | None to accurately reflect its potential nullability.
3. Logging: Added a logger.warning call when target_type is None to provide visibility into these cases in production logs without causing a serialization failure.
4. Regression Test: Added a new test case test_missing_target_type_does_not_raise to tests/sentry/incidents/serializers/test_workflow_engine_action.py to ensure that Action objects with a missing target_type in their config are serialized correctly without raising an error.

Legal Boilerplate

Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. and is gonna need some rights from me in order to utilize my contributions in this here PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

Fixes SENTRY-5QVV

_{Comment @sentry <feedback> on this PR to have Autofix iterate on the changes.}

[alexsohn1126]

hmmmmmm i kinda want tests here........ @sentry can u write some regression tests 👀

[sentry]

Bug: If target_identifier is None in the config, casting it to an int will cause a TypeError or ValueError, crashing the serializer.
_{Severity: HIGH}

Suggested Fix

Add a check to ensure target_identifier is not None before attempting to cast it to an integer. Provide a default value or handle the None case gracefully. For example, retrieve the value with target_identifier = obj.config.get("target_identifier") and then add a conditional check if target_identifier is not None: before calling int().

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: src/sentry/incidents/endpoints/serializers/workflow_engine_action.py#L79-L83

Potential issue: If an action's configuration in the database is missing the
`target_identifier` field, the serializer will fail. For actions of type `SENTRY_APP`,
an attempt to call `int(obj.config.get("target_identifier"))` will receive `None`,
raising a `TypeError`. For `PAGERDUTY` or `SENTRY_APP` actions, the code calls
`get_identifier_from_action` with `str(target_identifier)`. If `target_identifier` is
`None`, this becomes `int("None")`, which raises a `ValueError`. This scenario is
plausible in production, as evidenced by the similar bug for `target_type` that this
pull request aims to fix.

_{Did we get this right? 👍 / 👎 to inform future reviews.}

[sentry]

Bug: The serializer can crash with a ValueError when a PagerDuty or Sentry App action is missing a target_identifier, as it attempts to run int("None").
_{Severity: HIGH}

Suggested Fix

Before calling get_identifier_from_action, check if target_identifier is None. If it is, handle it gracefully, perhaps by returning None or a default value, to prevent the str() and subsequent int() conversion from crashing when the action type is PagerDuty or Sentry App.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: src/sentry/incidents/endpoints/serializers/workflow_engine_action.py#L84-L86

Potential issue: When serializing a PagerDuty or Sentry App action that is missing a
`target_identifier` in its configuration, the value defaults to `None`. This `None`
value is then cast to the string "None" and passed to the `get_identifier_from_action`
function. For PagerDuty or Sentry App action types, this function attempts to cast the
string "None" to an integer, which raises a `ValueError`. This scenario is likely for
older actions created before the field was required, and the incomplete fix in the pull
request fails to guard against it.

[github-actions]

Backend Test Failures

Failures on 990d765 in this run:

tests/sentry/incidents/serializers/test_workflow_engine_action.py::TestActionSerializer::test_missing_target_type_does_not_raise — log

[gw1] linux -- Python 3.13.1 /home/runner/work/sentry/sentry/.venv/bin/python3
tests/sentry/incidents/serializers/test_workflow_engine_action.py:200: in test_missing_target_type_does_not_raise
    self.critical_action.save()
src/sentry/silo/base.py:157: in override
    return original_method(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.venv/lib/python3.13/site-packages/django/db/models/base.py:902: in save
    self.save_base(
src/sentry/silo/base.py:157: in override
    return original_method(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.venv/lib/python3.13/site-packages/django/db/models/base.py:988: in save_base
    pre_save.send(
src/sentry/testutils/pytest/stale_database_reads.py:101: in send
    return old_send(self, sender, **named)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.venv/lib/python3.13/site-packages/django/dispatch/dispatcher.py:189: in send
    response = receiver(signal=self, sender=sender, **named)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
src/sentry/workflow_engine/receivers/action.py:18: in enforce_action_config_schema
    instance.validate_config(config_schema)
src/sentry/workflow_engine/models/json_config.py:17: in validate_config
    raise ValidationError(f"Invalid config: {e.message}")
E   jsonschema.exceptions.ValidationError: Invalid config: 'target_type' is a required property