From 3c31bb52099cdb4ccd6eed887723c5250514ef1d Mon Sep 17 00:00:00 2001
From: Suyash Kumar <suyashk@google.com>
Date: Fri, 12 Jul 2024 14:24:13 -0700
Subject: [PATCH] Fix issue with properties on null values inside queries.

This ensures the valueProperty helper also returns null on null value inputs.

PiperOrigin-RevId: 651886526
---
 interpreter/property.go         |  3 +++
 interpreter/property_test.go    | 38 ++++++++++++++++++++++++++++-----
 tests/enginetests/query_test.go |  6 ++++++
 3 files changed, 42 insertions(+), 5 deletions(-)

diff --git a/interpreter/property.go b/interpreter/property.go
index 31283b7..eba8251 100644
--- a/interpreter/property.go
+++ b/interpreter/property.go
@@ -60,6 +60,9 @@ func (i *interpreter) valueProperty(v result.Value, property string, staticResul
 	if property == "" {
 		return v, nil
 	}
+	if result.IsNull(v) {
+		return result.New(nil)
+	}
 
 	switch ot := v.GolangValue().(type) {
 	case result.Tuple:
diff --git a/interpreter/property_test.go b/interpreter/property_test.go
index 9de03f5..6d3b8c8 100644
--- a/interpreter/property_test.go
+++ b/interpreter/property_test.go
@@ -83,11 +83,6 @@ func TestEvalPropertyValue_Errors(t *testing.T) {
 			}),
 			resultType: &types.List{ElementType: types.Integer},
 		},
-		{
-			name:     "null",
-			property: "name",
-			value:    newOrFatal(t, nil),
-		},
 		{
 			name:     "interval invalid property",
 			property: "invalid",
@@ -119,6 +114,39 @@ func TestEvalPropertyValue_Errors(t *testing.T) {
 	}
 }
 
+func TestEvalPropertyValue(t *testing.T) {
+	tests := []struct {
+		name       string
+		property   string
+		value      result.Value
+		resultType types.IType
+		wantValue  result.Value
+	}{
+		{
+			name:      "property on null input value",
+			property:  "apple",
+			value:     newOrFatal(t, nil),
+			wantValue: newOrFatal(t, nil),
+		},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			i := &interpreter{
+				refs:                reference.NewResolver[result.Value, *model.FunctionDef](),
+				modelInfo:           newFHIRModelInfo(t),
+				evaluationTimestamp: time.Date(2024, 1, 1, 0, 0, 0, 0, time.UTC),
+			}
+			got, err := i.valueProperty(tc.value, tc.property, tc.resultType)
+			if err != nil {
+				t.Errorf("evalPropertyValue(%q) unexpected error: %v", tc.property, err)
+			}
+			if !got.Equal(tc.wantValue) {
+				t.Errorf("evalPropertyValue(%q) = %v, want %v", tc.property, got, tc.wantValue)
+			}
+		})
+	}
+}
+
 func newFHIRModelInfo(t *testing.T) *modelinfo.ModelInfos {
 	t.Helper()
 	fhirMIBytes, err := embeddata.ModelInfos.ReadFile("third_party/cqframework/fhir-modelinfo-4.0.1.xml")
diff --git a/tests/enginetests/query_test.go b/tests/enginetests/query_test.go
index 3ae4e81..956b67e 100644
--- a/tests/enginetests/query_test.go
+++ b/tests/enginetests/query_test.go
@@ -513,6 +513,12 @@ func TestQuery(t *testing.T) {
 				StaticType: &types.List{ElementType: &types.Tuple{ElementTypes: map[string]types.IType{"A": types.Integer, "B": types.Integer}}},
 			}),
 		},
+		{
+			// This ensures that properties on null values inside queries are handled correctly.
+			name:       "Property on null alias in query",
+			cql:        "define TESTRESULT: (null as Code) l return l.code",
+			wantResult: newOrFatal(t, nil),
+		},
 	}
 	for _, tc := range tests {
 		t.Run(tc.name, func(t *testing.T) {