[slominskir-coding-agent]

Fixes #51

What changed

/system-detail and /group-detail replied 500 (and logged EJBException: IllegalArgumentException: id to load is required for loading) when their ID was missing or empty, and the same for a non-number ID (NumberFormatException in ParamConverter). An ID that matched nothing rendered an empty page with a 200.

SystemDetail and GroupDetail now reply, through the app's /error page:

Request	Before	After
no ID, empty ID, abc	500	400
unknown ID (999999)	200, empty page	404
valid ID	200	200

PagesIT gets detailPageRejectsMissingOrUnknownId, covering those eight URLs.

No schema or settings changes, so there are no upgrade steps.

Checks

• ./gradlew build (compile + spotlessCheck): passed.
• New PagesIT cases against the unfixed app: all 8 failed (500 and 200, as above).
• My build ran as a side container (port 18443) on the dev stack's Oracle and Keycloak. ./gradlew integrationTest passed in full (all 41 PagesIT cases, plus MaskingRequestIT, ReadinessIT and StatusReportsIT).
• Server log: none of the requests above logged an ERROR. The only ERROR lines came from MaskingRequestIT's existing access-denied checks.
• Looked at screenshots taken with Puppet Show: group-detail?groupId=999999 shows the error page with "404: Not Found", and system-detail?systemId=141 still renders as before.
• CI's build doesn't run the integration tests; they need the running stack.

Decisions

• A non-number ID is treated like a missing one (400), following Checklists, which catches ParamConverter's exception and replies 400.
• sendError has no message: the app's error page shows only the status, so the other servlets don't pass one either.
• An unknown ID gets a 404 rather than the page's "not found" text, since the JSPs have no not-found state and the error page already shows "404: Not Found".

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