fix: pass None to rule evaluation when guardrail references missing field (#1406)

Co-authored-by: Valentina Bojan <valentina.bojan@uipath.com>

Author: valentinabojan

packages/uipath-core/pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "uipath-core"
-version = "0.5.5"
+version = "0.5.6"
 description = "UiPath Core abstractions"
 readme = { file = "README.md", content-type = "text/markdown" }
 requires-python = ">=3.11"

packages/uipath-core/src/uipath/core/guardrails/_evaluators.py

@@ -195,6 +195,9 @@ def evaluate_word_rule(
 ) -> tuple[bool, str]:
     """Evaluate a word rule against input and output data."""
     fields = get_fields_from_selector(rule.field_selector, input_data, output_data)
+    if not fields:
+        return True, "No fields to validate"
+
     operator = _humanize_guardrail_func(rule.detects_violation) or "violation check"
     field_paths = ", ".join({field_ref.path for _, field_ref in fields})
 
@@ -237,6 +240,9 @@ def evaluate_number_rule(
 ) -> tuple[bool, str]:
     """Evaluate a number rule against input and output data."""
     fields = get_fields_from_selector(rule.field_selector, input_data, output_data)
+    if not fields:
+        return True, "No fields to validate"
+
     operator = _humanize_guardrail_func(rule.detects_violation) or "violation check"
     field_paths = ", ".join({field_ref.path for _, field_ref in fields})
     for field_value, field_ref in fields:
@@ -281,6 +287,9 @@ def evaluate_boolean_rule(
 ) -> tuple[bool, str]:
     """Evaluate a boolean rule against input and output data."""
     fields = get_fields_from_selector(rule.field_selector, input_data, output_data)
+    if not fields:
+        return True, "No fields to validate"
+
     operator = _humanize_guardrail_func(rule.detects_violation) or "violation check"
     field_paths = ", ".join({field_ref.path for _, field_ref in fields})
     for field_value, field_ref in fields:

packages/uipath-core/tests/guardrails/test_deterministic_guardrails_service.py

@@ -1466,3 +1466,104 @@ def _create_guardrail_with_always_rule(
                 ),
             ],
         )
+
+
+class TestMissingFieldPassesValidation:
+    """Test that rules referencing missing fields pass validation."""
+
+    def test_word_rule_missing_field_passes(
+        self, service: DeterministicGuardrailsService
+    ) -> None:
+        guardrail = DeterministicGuardrail(
+            id="test-missing-field",
+            name="Missing Field Guardrail",
+            description="Test missing field",
+            enabled_for_evals=True,
+            guardrail_type="custom",
+            selector=GuardrailSelector(
+                scopes=[GuardrailScope.TOOL], match_names=["test"]
+            ),
+            rules=[
+                WordRule(
+                    rule_type="word",
+                    field_selector=SpecificFieldsSelector(
+                        selector_type="specific",
+                        fields=[
+                            FieldReference(path="sentence2", source=FieldSource.INPUT)
+                        ],
+                    ),
+                    detects_violation=lambda s: len(s or "") > 0,
+                    rule_description="sentence2 is not empty",
+                ),
+            ],
+        )
+        result = service._evaluate_deterministic_guardrail(
+            input_data={"sentence1": "hello"},
+            output_data={},
+            guardrail=guardrail,
+        )
+        assert result.result == GuardrailValidationResultType.PASSED
+
+    def test_number_rule_missing_field_passes(
+        self, service: DeterministicGuardrailsService
+    ) -> None:
+        guardrail = DeterministicGuardrail(
+            id="test-missing-field",
+            name="Missing Field Guardrail",
+            description="Test missing field",
+            enabled_for_evals=True,
+            guardrail_type="custom",
+            selector=GuardrailSelector(
+                scopes=[GuardrailScope.TOOL], match_names=["test"]
+            ),
+            rules=[
+                NumberRule(
+                    rule_type="number",
+                    field_selector=SpecificFieldsSelector(
+                        selector_type="specific",
+                        fields=[FieldReference(path="age", source=FieldSource.INPUT)],
+                    ),
+                    detects_violation=lambda n: n is not None and n < 0,
+                    rule_description="age is negative",
+                ),
+            ],
+        )
+        result = service._evaluate_deterministic_guardrail(
+            input_data={"name": "test"},
+            output_data={},
+            guardrail=guardrail,
+        )
+        assert result.result == GuardrailValidationResultType.PASSED
+
+    def test_boolean_rule_missing_field_passes(
+        self, service: DeterministicGuardrailsService
+    ) -> None:
+        guardrail = DeterministicGuardrail(
+            id="test-missing-field",
+            name="Missing Field Guardrail",
+            description="Test missing field",
+            enabled_for_evals=True,
+            guardrail_type="custom",
+            selector=GuardrailSelector(
+                scopes=[GuardrailScope.TOOL], match_names=["test"]
+            ),
+            rules=[
+                BooleanRule(
+                    rule_type="boolean",
+                    field_selector=SpecificFieldsSelector(
+                        selector_type="specific",
+                        fields=[
+                            FieldReference(path="is_active", source=FieldSource.INPUT)
+                        ],
+                    ),
+                    detects_violation=lambda b: b is False,
+                    rule_description="is_active is false",
+                ),
+            ],
+        )
+        result = service._evaluate_deterministic_guardrail(
+            input_data={"name": "test"},
+            output_data={},
+            guardrail=guardrail,
+        )
+        assert result.result == GuardrailValidationResultType.PASSED