fix: is_allowed answers FALSE for a NULL user instead of failing on auth_cache

tests/18_null_user.sql

@@ -0,0 +1,29 @@
+-- =============================================================================
+-- NULL user Tests
+-- =============================================================================
+-- is_allowed() and is_allowed_nocache() answer FALSE for a NULL user id, as
+-- rls_check() does, instead of failing on the auth_cache NOT NULL constraint.
+--
+-- Prerequisites: 00_setup.sql -> 17_is_allowed_equivalence.sql
+-- =============================================================================
+
+\echo ''
+\echo '================================================================'
+\echo '18 -- NULL USER'
+\echo '================================================================'
+
+SELECT morbac.t('is_allowed NULL user, org',
+    morbac.is_allowed(NULL, '10000000-0000-0000-0000-000000000001'::uuid, 'read', 'documents'),
+    FALSE);
+
+SELECT morbac.t('is_allowed NULL user, no org',
+    morbac.is_allowed(NULL, NULL, 'read', 'documents'),
+    FALSE);
+
+SELECT morbac.t('is_allowed_nocache NULL user, org',
+    morbac.is_allowed_nocache(NULL, '10000000-0000-0000-0000-000000000001'::uuid, 'read', 'documents'),
+    FALSE);
+
+SELECT morbac.t('is_allowed NULL user writes nothing to auth_cache',
+    NOT EXISTS (SELECT 1 FROM morbac.auth_cache WHERE user_id IS NULL),
+    TRUE);