fix(detectors): Safely access queryObj for cron monitors

[sentry]

This PR addresses a TypeError: Cannot read properties of null (reading 'config') that occurs when detector.dataSources[0].queryObj is null for certain cron detectors.

The root cause was identified as queryObj being null at runtime for some cron detectors, despite the TypeScript type indicating it as non-null. The UI components were attempting to access properties like .config, .id, or .environments directly on a potentially null queryObj, leading to crashes.

This fix implements optional chaining (?.) and null checks in the following locations:

• static/app/views/detectors/components/detectorLink.tsx: In CronDetectorDetails, config is now accessed safely, and the component returns null if config is undefined.
• static/app/views/detectors/list/cron.tsx: In VisualizationCell, cronId and cronEnvironments are now safely extracted using optional chaining. The useMonitorStats hook is updated to handle a potentially null cronId.
• static/app/views/detectors/list/cron.tsx: The environment column rendering now safely accesses environments using optional chaining, preventing crashes when queryObj is null.

These changes ensure the UI gracefully handles cases where queryObj is absent, preventing TypeErrors and improving stability.

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Fixes JAVASCRIPT-39QG

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

Unsafe map on environments

High Severity

When queryObj is null, optional chaining yields undefined for environments, but .map is still invoked on that value. That throws the same class of runtime error this PR targets, so the environment column can still crash for cron detectors without a queryObj.

 

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[sentry]

Bug: Incomplete optional chaining on environments will cause a crash when queryObj is null. The .map() function will be called on an undefined value, throwing a TypeError.
_{Severity: HIGH}

Suggested Fix

Add optional chaining before the .map() call to safely handle cases where environments is undefined. The line should be changed to {detector.dataSources[0]?.queryObj?.environments?.map(environment => { ... });}.

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: static/app/views/detectors/list/cron.tsx#L112

Potential issue: In the environment column renderer, the code accesses
`detector.dataSources[0]?.queryObj?.environments.map(...)`. While optional chaining is
used for `queryObj`, it is not used before the `.map()` call. The pull request's context
confirms that `queryObj` can be `null` at runtime. In such cases,
`detector.dataSources[0]?.queryObj?.environments` evaluates to `undefined`. Attempting
to call `.map()` on `undefined` will result in a `TypeError: Cannot read properties of
undefined (reading 'map')`, causing a crash in the UI component when rendering the
environment column for a detector with a null `queryObj`.

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