diff --git a/finbot/core/data/models.py b/finbot/core/data/models.py
index d01c2e65..39f6b909 100644
--- a/finbot/core/data/models.py
+++ b/finbot/core/data/models.py
@@ -397,6 +397,11 @@ def to_dict(self) -> dict:
             except (ValueError, TypeError):
                 pass
 
+        if self.invoice_date is None:
+            raise ValueError(f"Invoice {self.id} has no invoice_date set")
+        if self.due_date is None:
+            raise ValueError(f"Invoice {self.id} has no due_date set")
+
         return {
             "id": self.id,
             "namespace": self.namespace,
diff --git a/tests/unit/data/__init__.py b/tests/unit/data/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/unit/data/test_invoice_model.py b/tests/unit/data/test_invoice_model.py
new file mode 100644
index 00000000..7a69d315
--- /dev/null
+++ b/tests/unit/data/test_invoice_model.py
@@ -0,0 +1,70 @@
+"""Tests for Invoice.to_dict's date-field null handling.
+
+GitHub issues #290 (Bug_107, PAY-FIELD-001) and #291 (Bug_108,
+PAY-FIELD-002): Invoice.to_dict calls .isoformat() directly on
+invoice_date and due_date with no null guard, so a row with either field
+missing raises an unhandled AttributeError instead of a clear error --
+and since get_invoice_for_payment (finbot/tools/data/payment.py) calls
+to_dict() directly, the crash propagates straight into payment
+processing with no useful diagnostic.
+
+Verified against source before writing anything: finbot/core/data/
+models.py's Invoice.to_dict (lines ~391-414) has no guard on either
+field. Both columns are declared nullable=False in the schema, so this
+is only reachable via corrupted/anomalous data (e.g. a raw SQL write
+bypassing the ORM) -- but when it happens, the fix should raise a clear,
+diagnosable ValueError rather than crash with an opaque AttributeError,
+per the issues' own acceptance criteria.
+"""
+
+import pytest
+from datetime import UTC, datetime
+
+from finbot.core.data.models import Invoice
+
+
+def _make_invoice(invoice_date, due_date):
+    now = datetime.now(UTC)
+    return Invoice(
+        id=1,
+        namespace="ns_test",
+        vendor_id=1,
+        invoice_number="1",
+        amount=100.0,
+        description="test invoice",
+        invoice_date=invoice_date,
+        due_date=due_date,
+        status="approved",
+        agent_notes=None,
+        attachments=None,
+        created_at=now,
+        updated_at=now,
+    )
+
+
+class TestInvoiceToDictDateHandling:
+
+    @pytest.mark.unit
+    def test_pay_field_001_to_dict_raises_clear_error_when_invoice_date_is_none(self):
+        invoice = _make_invoice(invoice_date=None, due_date=datetime.now(UTC))
+
+        with pytest.raises(ValueError, match="invoice_date"):
+            invoice.to_dict()
+
+    @pytest.mark.unit
+    def test_pay_field_002_to_dict_raises_clear_error_when_due_date_is_none(self):
+        invoice = _make_invoice(invoice_date=datetime.now(UTC), due_date=None)
+
+        with pytest.raises(ValueError, match="due_date"):
+            invoice.to_dict()
+
+    @pytest.mark.unit
+    def test_to_dict_works_normally_when_both_dates_present(self):
+        """Regression: ordinary invoices with valid dates must be unaffected."""
+        now = datetime.now(UTC)
+        invoice = _make_invoice(invoice_date=now, due_date=now)
+
+        result = invoice.to_dict()
+
+        assert result["invoice_date"] == now.isoformat().replace("+00:00", "Z")
+        assert result["due_date"] == now.isoformat().replace("+00:00", "Z")