lib/reqmgrsystems/reqMgrSystemEdit.php?doAction=edit&id=<id that does not exist> answered HTTP 200 with a broken edit form (empty name/type/cfg) and wrote 5 E_WARNING (log_level=2) rows into events on every request. An existing id wrote 0 rows — the warnings were id-specific.

The report predates commit 3897a17c8 (feat(#1727), 2026-09-29 22:18Z), which replaced the whole legacy page with a session-guarded 302 shim. Verified on a fresh DB (login admin/admin, branch fix/issue-1721-edit-missing-id):

The browser followed the 302; the modern editor then called GET /api/reqmgrsystemedit/index.php?action=init&id=99999&prune=1 → 404 {"status":"error","code":"not_found","message":"Requirement management system not found"}, rendering the localized “Requirement management system not found” state (screenshot above).

events after the whole matrix: 1 row (the login audit_login_succeeded, log_level=16) — i.e. 0 new Error/Warning rows. The reported 200-broken-form + 5-warning behaviour is not reproducible.

Blast radius: reqMgrSystemCommands is orphaned dead code — grep -rn reqMgrSystemCommands returns only its own file plus comments in the shim. Its create() (line 107) already builds a safe zeroed entity, and tlReqMgrSystem::checkConnection() was hardened for exactly this getByID()==null return in #1625 (tlReqMgrSystem.class.php:738, is_null($xx) || !isset(...)). edit() was the one remaining unguarded caller of getByID() in this screen's family. No other screen shares the path, so there is no regression surface.

--- a/lib/reqmgrsystems/reqMgrSystemCommands.class.php
+++ b/lib/reqmgrsystems/reqMgrSystemCommands.class.php
@@ edit()
-    $guiObj->item = $this->mgr->getByID($argsObj->id);
+    $item = $this->mgr->getByID($argsObj->id);
+    if( is_null($item) )
+    {
+      $item = array('id' => 0);
+      foreach($this->entitySpec as $property => $type)
+      {
+        $item[$property] = ($type == 'int') ? 0 : '';
+      }
+      $guiObj->item = $item;
+      $guiObj->template = "reqMgrSystemView.php";
+      return $guiObj;
+    }
+
+    $guiObj->item = $item;
     $guiObj->canManage = $argsObj->currentUser->hasRight($this->db,'reqmgrsystem_management');
     return $guiObj;

A missing id now degrades to a well-formed empty entity (the same shape create() builds) and a redirect to the list screen, instead of handing a null to the renderer. The non-null path is unchanged.

Alternatives rejected

• Deleting the orphaned class + the two dead .tpl files — a larger, drive-by cleanup; the issue is a hardening request, and a guard is the minimal change that removes the named defect (same reasoning as #1625's guard).
• Re-pointing the shim to an old-style render — would re-open the pre-#1727 behaviour; explicitly out of scope.
• Adding a new i18n “not found” message key — unnecessary: the modern editor owns the user-facing 404; the legacy class is unreachable.

• php -l lib/reqmgrsystems/reqMgrSystemCommands.class.php → No syntax errors detected.
• Legacy ?doAction=edit&id=99999 → 302; ?doAction=edit&id=2 → 302; bare URL → 302.
• Modern GET /api/reqmgrsystemedit/?action=init&id=99999 → 404 not_found.
• SELECT count(*) total, sum(log_level<4) warn_or_err FROM events → total=1, warn_or_err=0.
• Regression suite Regression — Issue #1721 in tmp/TLU_Test_Cases.md, all cases PASS; gate TLU_REQUIRE_SUITE="Issue #1721" bash ai/verify_test_suites.sh → 7 PASS / 0 FAIL, exit 0.

• lib/reqmgrsystems/reqMgrSystemCommands.class.php — null guard in edit().
• CHANGELOG — one dated 2.0.1 line.
• tmp/TLU_Test_Cases.md — regression suite (git-ignored, appended).

No i18n bundle, no template, no BFF file, no DB change.

php -l lib/reqmgrsystems/reqMgrSystemCommands.class.php
# login, then:
curl -s -D - -o /dev/null -b c.txt \
  "http://localhost:8082/lib/reqmgrsystems/reqMgrSystemEdit.php?doAction=edit&id=99999"
# -> HTTP/1.1 302 Found -> .../reqMgrSystemEdit.html?id=99999
curl -s -o /dev/null -w '%{http_code}\n' -b c.txt \
  "http://localhost:8082/api/reqmgrsystemedit/index.php?action=init&id=99999"
# -> 404
mysql -h 127.0.0.1 -utestlink -ptestlink testlink \
  -e "SELECT count(*) total, sum(log_level<4) warn_or_err FROM events;"
# -> 0 Error/Warning rows

Browser: log in admin/admin, open gui/templates/reqmgrsystems/reqMgrSystemEdit.html?id=99999 → localized “Requirement management system not found”; Event Viewer stays clean.