Loading the LEGACY compare page lib/testcases/tcCompareVersions.php without a valid testcase_id (e.g. ?tproject_id=1) logs 2x E_WARNING Trying to access array offset on null (events table, log_level 2, activity=PHP), both pointing to Line 121. The HTTP response stays 200 — the symptom is only visible in the Event Viewer / events table.

Reproduce at HEAD (measured on the fresh-import CI box): with an authenticated session call

curl -b <cookies> ".../lib/testcases/tcCompareVersions.php?tproject_id=1"

→ HTTP 200, and two E_WARNING rows appear in events: E_WARNING\nTrying to access array offset on null - in .../lib/testcases/tcCompareVersions.php - Line 121 (log_level=2).

• init_args() (tcCompareVersions.php:87) sets $args->tcase_id = intval($_REQUEST['testcase_id'] ?? 0) → 0 when the parameter is absent.
• initializeGUI() (tcCompareVersions.php:120) calls $tcaseMgr->get_by_id(0); testcase::get_by_id() (lib/functions/testcase.class.php:2749) builds WHERE NHTCV.parent_id = 0 and returns null (no rows).
• tcCompareVersions.php:121 $gui->tcaseName = $gui->tc_versions[0]['name']; dereferences null → 2x E_WARNING (PHP 8 fires the array-offset-on-null warning twice for the same expression in this context).

Blast radius: the deref is file-local (initializeGUI is invoked once at tcCompareVersions.php:24). The dashio Smarty template gui/templates/dashio/testcases/tcCompareVersions.tpl tolerates a null tc_versions in its {foreach} (renders the empty "select versions" form), so the page remains functional without a testcase. The modern tcCompare.html screen (Refs #809 / #1327) has a separate BFF (api/testcasescompare/index.php) and is unaffected.

Committed on branch fix/issue-1332, commit 9fbcf3533:

$gui->tc_versions = $tcaseMgr->get_by_id($argsObj->tcase_id);
$gui->tcaseName = isset($gui->tc_versions[0]['name']) ? $gui->tc_versions[0]['name'] : '';

The guard means "no testcase selected" now degrades gracefully to an empty tcaseName (the compare subtitle simply shows an empty label slot), matching the suggested fix in the issue. Valid requests behave identically: get_by_id() returns the full row map for an existing testcase, so the guard never trips. No new user-facing strings → no locale-bundle additions.

Rejected alternatives: (a) early-return / displayInfo() "select a test case" page — a behavior change beyond a log-noise bug, and the legacy page already renders the selection form fine; (b) guarding buildDiff() intake — that is a separate code path (compare_selected_versions=1 submitted with no testcase triggers foreach() argument must be of type array|object, null given at Line 157), filed as a distinct bug (see below) so this fix stays minimal and scoped to the reported Line 121 warnings.

Related issue filed during this run: #1333 — same repro family (null get_by_id when no testcase selected) but a different crash site (buildDiff() Line 157 foreach on null), reachable only via crafted compare_selected_versions=1&testcase_id=0 requests. Left open by design per the one-bug-per-run rule.

• lib/testcases/tcCompareVersions.php — initializeGUI(), line 121: isset(...) guard with '' fallback.
• tmp/TLU_Test_Cases.md — regression suite "Regression — Issue #1332", 7/7 PASS.

All checks on branch fix/issue-1332, PHP 8.3, MySQL 11.4 testlink fresh-import schema:

• Repro ?tproject_id=1 (no testcase_id), pre-fix = 2 E_WARNING rows at Line 121 → post-fix HTTP 200, page renders "Testcase versions compare page" + empty version-selection form, 0 new log_level IN (2,3) rows.
• Happy path: 2-version testcase fixture (node 3, tcversions 4/5), open ?tproject_id=1&testcase_id=3 → HTTP 200, both version radios (1 and 2) rendered, subtitle populated, 0 new warnings.
• TEXT compare path testcase_id=3&version_left=1&version_right=2&compare_selected_versions=1 → HTTP 200, diff rendered, 0 new warnings.
• Headless-Chrome browser open of the no-testcase URL → no JS/console errors beyond a pre-existing generic "Deprecated feature used" notice; screenshot tcCompareVersions-no-tcase-id-fixed.png below.
• Event Viewer after the whole pass → only INFO/AUDIT (audit_login_succeeded, log_level 16); SELECT COUNT(*) FROM events WHERE log_level IN (2,3) = 0.

Regression suite: tmp/TLU_Test_Cases.md — "Regression — Issue #1332", 7/7 PASS.

Address: Fixes #1332 (verified + pushed on fix/issue-1332).