While seeding fixtures for the Requirement Viewer modernization (Refs #755), the Event Viewer gained ERROR + E_WARNING entries every time a requirement node id could not be resolved to a requirement spec (e.g. absent/deleted requirement, or a top-level node whose parent id is not resolvable).

The events table captured, per offending call:

ERROR ON exec_query() ... 1064 ... /* Class:requirement_spec_mgr - Method:
get_last_child_info */ SELECT COALESCE(MAX(revision),-1) AS revision FROM
req_specs_revisions CHILD, nodes_hierarchy NH WHERE NH.id = CHILD.id
AND NH.parent_id =            <- empty parent id

plus

E_WARNING Trying to access array offset on null
  - lib/functions/requirement_mgr.class.php:3434

requirement_mgr::getTestProjectID($id, $reqSpecID=null) (lib/functions/requirement_mgr.class.php:3427), when $reqSpecID is null, calls get_node_hierarchy_info($id) and then assigns $parent = $dummy['parent_id'] (:3434) without checking $dummy for null. When the node is not found, get_node_hierarchy_info() returns null (tree.class.php:225), so:

1. $dummy['parent_id'] emits E_WARNING: Trying to access array offset on null.
2. $parent becomes null.
3. requirement_spec_mgr::get_by_id($parent) is called with null (requirement_mgr.class.php:3436), and get_by_id() calls get_last_child_info($id) (requirement_spec_mgr.class.php:185).
4. get_last_child_info($id) (requirement_spec_mgr.class.php:2165) interpolates the raw $id into AND NH.parent_id = {$id} without any validation → an empty id produces NH.parent_id = → SQL syntax error 1064.

Two minimal, defensive guards — no refactoring:

1. lib/functions/requirement_mgr.class.php — getTestProjectID()

Guard the $dummy result from get_node_hierarchy_info() before reading parent_id, and return null (instead of crashing) when the project cannot be derived, and tolerate a missing testproject_id in the target:

$parent = $reqSpecID;
if( is_null($parent) )
{
  $dummy = $this->tree_mgr->get_node_hierarchy_info($id);
  if( !is_null($dummy) && isset($dummy['parent_id']) )
  {
    $parent = $dummy['parent_id'];
  }
}
if( is_null($parent) )
{
  // id did not resolve to a requirement spec => cannot derive project
  return null;
}
$target = $reqSpecMgr->get_by_id($parent);
return isset($target['testproject_id']) ? $target['testproject_id'] : null;

2. lib/functions/requirement_spec_mgr.class.php — get_last_child_info()

Defense in depth for every caller: reject an invalid $id (null / empty / non-numeric / <= 0) and an unknown child_type before building the SQL, so a broken NH.parent_id = <empty> clause can never be emitted:

$child_type = $my['options']['child_type'];
if( !isset($target_cfg[$child_type]) || is_null($id) || $id === '' || !is_numeric($id) || intval($id) <= 0 )
{
    return null;
}

• Guard at the source (getTestProjectID) — removes both the E_WARNING and the null-$parent propagation in one place. Rejected alternative: only fixing get_last_child_info would have silenced the SQL error but left the E_WARNING Trying to access array offset on null intact.
• Early-return in get_last_child_info — protects all 6+ call sites in the requirement classes from ever passing an empty id into interpolated SQL. Rejected alternative: casting/escaping $id inside the SQL still tried to execute a query with a parent_id that does not exist, which is semantically wrong and still emits a (harmless) DB round-trip; returning null is the correct "no such child" signal that callers already handle.

• Negative (bug) path: $reqMgr->getTestProjectID(999999) → returns NULL; events table gains 0 ERROR / 0 E_WARNING rows (previously 2 rows per call).
• Defense-in-depth: get_last_child_info(null|''|'abc'|0|-5) → all return null; events table gains 0 rows.
• Positive (regression) path: created test project + top-level req spec 'Order Management Spec' + requirements RM-001..003 (exact seed scenario) — all created successfully, getTestProjectID(valid req) still returns the correct testproject_id; only the expected audit CREATE event (log_level=16), zero ERROR/WARNING.
• php -l passes on both modified files.
• Code review: PASS (correct, minimal, no regressions, no i18n needed — pure backend guards).
• 4 regression test cases in tmp/TLU_Test_Cases.md (suite 765) — all PASS.

• lib/functions/requirement_mgr.class.php (getTestProjectID, +8/-1)
• lib/functions/requirement_spec_mgr.class.php (get_last_child_info, +7)

• 235a31425 — fix(requirements): guard getTestProjectID + get_last_child_info against null/empty ids — Refs #765

• 7ac1332c6 — test: regression suite 765 — Refs #765

• Event Viewer clean after fix: ERROR=0, WARNING=0.