diff --git a/.changeset/validation-null-omitted-insert.md b/.changeset/validation-null-omitted-insert.md
new file mode 100644
index 0000000000..695fdcb526
--- /dev/null
+++ b/.changeset/validation-null-omitted-insert.md
@@ -0,0 +1,15 @@
+---
+"@objectstack/objectql": patch
+---
+
+fix(objectql): `record.<field> == null` validation fires on insert when the field is omitted (#1871)
+
+A `script` / `cross_field` validation predicate like `record.due_date == null`
+did not fire on **insert** when the optional field was omitted entirely from the
+payload — the CEL `record` scope lacked the key, so `record.x == null` saw a
+missing key (not null) and silently couldn't match. It worked on update (the
+prior record supplies the field) and when the field was explicitly `null`.
+
+Fix: on insert, default declared-but-absent schema fields to `null` in the rule
+evaluation scope, so an omitted optional reads as `null` — matching an explicit
+`null` and the update path.
diff --git a/packages/objectql/src/validation/rule-null-omitted.test.ts b/packages/objectql/src/validation/rule-null-omitted.test.ts
new file mode 100644
index 0000000000..6f19ed7edc
--- /dev/null
+++ b/packages/objectql/src/validation/rule-null-omitted.test.ts
@@ -0,0 +1,48 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * #1871 — a `record.<field> == null` predicate must fire on INSERT when the
+ * optional field is omitted entirely from the payload (key absent), the same
+ * way it fires when the field is explicitly `null`. Before the fix the CEL
+ * `record` scope on insert lacked the key, so `record.x == null` could not match.
+ */
+import { describe, it, expect } from 'vitest';
+import { evaluateValidationRules } from './rule-validator';
+
+const schema = {
+  fields: {
+    priority: { name: 'priority', label: 'Priority', type: 'text' },
+    due_date: { name: 'due_date', label: 'Due', type: 'date' },
+  },
+  validations: [
+    {
+      name: 'urgent_needs_due',
+      type: 'script',
+      condition: 'record.priority == "urgent" && record.due_date == null',
+      message: 'Urgent tasks require a due date',
+      events: ['insert', 'update'],
+    },
+  ],
+} as any;
+
+describe('validation: `field == null` on insert with omitted field (#1871)', () => {
+  it('fires when due_date is OMITTED from the insert payload', () => {
+    expect(() => evaluateValidationRules(schema, { priority: 'urgent' }, 'insert', {}))
+      .toThrow(/rule_violation|_record|Validation failed/);
+  });
+
+  it('fires when due_date is explicitly null (already worked)', () => {
+    expect(() => evaluateValidationRules(schema, { priority: 'urgent', due_date: null }, 'insert', {}))
+      .toThrow(/rule_violation|_record|Validation failed/);
+  });
+
+  it('does NOT fire when due_date is present', () => {
+    expect(() => evaluateValidationRules(schema, { priority: 'urgent', due_date: '2026-01-01' }, 'insert', {}))
+      .not.toThrow();
+  });
+
+  it('does NOT fire when priority is not urgent', () => {
+    expect(() => evaluateValidationRules(schema, { priority: 'low' }, 'insert', {}))
+      .not.toThrow();
+  });
+});
diff --git a/packages/objectql/src/validation/rule-validator.ts b/packages/objectql/src/validation/rule-validator.ts
index c2874eea51..5f8a0c9751 100644
--- a/packages/objectql/src/validation/rule-validator.ts
+++ b/packages/objectql/src/validation/rule-validator.ts
@@ -263,6 +263,16 @@ export function evaluateValidationRules(
   // Merged view used by predicate rules: prior state overlaid with the PATCH,
   // so a rule referencing an unchanged field still sees its persisted value.
   const merged: Record<string, unknown> = { ...(previous ?? {}), ...data };
+  // #1871 — on INSERT, a field omitted entirely from the payload is absent from
+  // the record, so a `record.x == null` predicate sees a missing CEL key (which
+  // does not equal null) and silently can't match. Default declared-but-absent
+  // fields to null so an omitted optional reads as null — matching an explicit
+  // `null` and the UPDATE path (where the prior record already supplies them).
+  if (mode === 'insert' && fields) {
+    for (const name of Object.keys(fields)) {
+      if (!(name in merged)) merged[name] = null;
+    }
+  }
   const ctx: RuleContext = { data, merged, previous, mode, logger: opts.logger };
 
   const errors: FieldValidationError[] = [];