Issue 555 — tlIssueTracker::getInterfaceObject(): PHP 8 array-offset-on-null for orphaned tracker link

Issue: #555 Branch: fix/issue-555 Status: VERIFIED-FIXED & CLOSED (2026-08-25)

Symptom

With issue_tracker_enabled=1 on a project, if the referenced issuetrackers row is deleted (orphaned FK — schema does not enforce foreign keys), any caller of tlIssueTracker::getInterfaceObject() (print, execSetResults, bugAdd, mainPage, resultsBugs, etc.) could trigger:

E_WARNING: Trying to access array offset on null
  in lib/functions/tlIssueTracker.class.php - Line 690

Found during code review of #553 — the #553 fix guarded $issueT but left a downstream dereference of $itd unguarded.

Root cause chain & fix approach (the HOW)

1. getInterfaceObject() calls $this->getLinkedTo($tprojectID) (line 672) which uses INNER JOIN on issuetrackers — returns non-null only when both testproject_issuetracker and issuetrackers rows exist.

2. The #553 fix (commit 4f841bb91) added null guard for $issueT at lines 675 and 687, preventing the first unguarded dereference ($issueT['issuetracker_name']).

3. But at line 689: $itd = $this->getByID($issueT['issuetracker_id']) — getByID() (line 344) queries issuetrackers table independently via getByAttr() which returns null if no row matches.

4. At line 690: $iname = $itd['implementation'] — unguarded array access on potentially null $itd → PHP 8 E_WARNING.

The INNER JOIN in getLinkedTo() means the orphaned-link race condition is unlikely in normal operation (the JOIN filters out missing rows). However, a race condition is possible: getLinkedTo() succeeds (tracker exists at query time), then getByID() runs (tracker deleted between the two queries). The unguarded dereference is a latent defect regardless.

Fix: Added is_null($itd) guard at line 689-693 returning null early when tracker data is missing. This prevents the unguarded array access and is consistent with the existing null guard pattern from #553.

Why this approach: minimal 4-line addition, matches the existing guard pattern, returns null which all 14 callers of getInterfaceObject() handle gracefully (except bugAdd.php:293-302 which has a pre-existing unguarded downstream use — tracked separately). Alternatives rejected: throwing an exception (too invasive for a defensive guard), logging and continuing (would still crash on new $iname()).

Files changed

File	Change
lib/functions/tlIssueTracker.class.php	Added is_null($itd) guard after getByID() at line 689, returning null early (+4 lines)

Verification performed (2026-08-25)

Environment: fresh DB, app http://localhost:8082, admin/admin, headless Chrome, project 1 "TestProject555" with issue_tracker_enabled=1.

Check	Result
php -l lib/functions/tlIssueTracker.class.php	No syntax errors
Navigate to index.php?tproject_id=1 with valid tracker	Page loads, no console errors, 0 new Event Viewer entries
Delete issuetrackers row (orphan link), navigate to index.php?tproject_id=1	Page loads, no E_WARNING at line 690, 0 new Event Viewer entries
Code review subagent	Fix correct, no other unguarded $itd dereferences in method

Regression suite: tmp/TLU_Test_Cases.md → "Regression — Issue #555" (2/2 PASS).