Fixed: clicking Save for baseline (or deep-linking lib/results/resultsByTSuite.php?tplan_id=<plan>&format=0&doAction=saveForBaseline) on a test plan that has linked level-2 suites but zero executions crashed the page with a raw DB Access Error backtrace and polluted the Event Viewer:

E_WARNING Trying to access array offset on null - resultsByTSuite.php   (x3)
DATABASE ERROR ON exec_query() - 1064 You have an error in your SQL syntax...

This is the follow-up flagged by #587 (which deliberately fixed only the render path to stay minimal).

saveForBaseline consumed $gui->spanByPlatform without checking that span data exists. On a plan with no execution rows, getExecTimeSpan() returns null (aggregate query yields no rows), so after the #587 guard $gui->spanByPlatform[$platID] is null. The save block then did:

$span = $gui->spanByPlatform[$platID];          // null -> E_WARNING
$sql = "INSERT ... VALUES({$span['testplan_id']}, {$platID}, '{$span['begin']}', '{$span['end']}')";

Each null-offset read raised "Trying to access array offset on null", and the three values interpolated as empty strings, producing invalid SQL (VALUES(,0,'','')) → SQL 1064 → DB Access Error page. On setups where the INSERT could run, empty begin/end timestamps would be written into baseline_l1l2_context, corrupting baseline data.

One guard at each level of the save block (lib/results/resultsByTSuite.php):

if ($args->doAction == 'saveForBaseline') {
  $gui->baselineSaved = false;
  if( isset($gui->dataByPlatform) && !is_null($gui->dataByPlatform) ) {  // report data absent?
    $savedSomething = false;
    foreach ($gui->dataByPlatform->testsuites as $platID => $elem) {
      // no execution records for this platform => nothing to baseline
      if( !isset($gui->spanByPlatform[$platID]) ||
          is_null($gui->spanByPlatform[$platID]) ) {
        continue;
      }
      ... // unchanged INSERTs ...
      $savedSomething = true;
    }
    if( $savedSomething ) {
      $gui->baselineSaved = true;                 // success feedback only when real data saved
    } else {
      $gui->do_report['status_ok'] = 0;
      $gui->do_report['msg'] = lang_get('baseline_save_no_executions');
    }
  }
}

Why this shape:

• isset() / is_null() are warning-free under PHP 8 on possibly-null array offsets — same technique already used by #587 on the render path.
• The per-platform check keeps partial saves working: in a multi-platform plan where only some platforms have executions, executed platforms are baselined, idle ones are skipped.
• $gui->baselineSaved = true now fires only when something was actually saved, so the "Baseline saved" confirmation can no longer lie.
• When nothing was saved the screen reuses its existing error channel ($gui->do_report), which both themes (dashio / tl-classic) already render.
• Alternatives rejected: aborting before the loop on is_null($gui->spanByPlatform) alone would miss the no-platform [0] => null shape and mixed-platform plans.

i18n: new key $TLS_baseline_save_no_executions added to locale/en_GB/strings.txt and locale/en_US/strings.txt ("Baseline NOT saved: the test plan has no execution records yet. Execute at least one test case, then save the baseline again."). All other locales fall back to en_GB via lang_get(). No hardcoded strings in code.

Fixture: project 1 / plan 10 / build 300 / nested suites TopSuite > ChildSuite / TC-589 v1 linked, zero executions.

Regression suite: Regression — Issue #589 in tmp/TLU_Test_Cases.md.

• lib/results/resultsByTSuite.php — guards around the whole saveForBaseline block (~90-146)
• locale/en_GB/strings.txt — $TLS_baseline_save_no_executions
• locale/en_US/strings.txt — same key