Correctly error for mixed units where one is an empty unit string

interpreter/operator_aggregate.go

@@ -310,19 +310,22 @@ func (i *interpreter) evalMedianQuantity(_ model.IUnaryExpression, operand resul
 
 	values := make([]float64, 0, len(l))
 	var unit model.Unit
-	for _, elem := range l {
+	for idx, elem := range l {
 		if result.IsNull(elem) {
 			continue
 		}
 		v, err := result.ToQuantity(elem)
 		if err != nil {
 			return result.Value{}, err
 		}
-		// We only support List<Quantity> where all the elements have the exact same unit, since we do not support
-		// mixed unit Quantity math in our engine yet.
-		if unit == "" {
+		// We only support List<Quantity> where all the elements have the exact same unit, since we
+		// do not support mixed unit Quantity math in our engine yet.
+		if idx == 0 {
 			unit = v.Unit
-		} else if unit != v.Unit {
+		}
+		if unit != v.Unit {
+			// TODO: b/342061715 - technically we should treat '' unit and '1' unit as the same, but
+			// for now we don't (and we should apply this globally).
 			return result.Value{}, fmt.Errorf("Median(List<Quantity>) operand has different units which is not supported, got %v and %v", unit, v.Unit)
 		}
 		values = append(values, v.Value)

tests/enginetests/operator_aggregate_test.go

@@ -680,6 +680,11 @@ func TestMedian_Error(t *testing.T) {
 			cql:             "Median({1 'cm', 2 'g'})",
 			wantErrContains: "Median(List<Quantity>) operand has different units which is not supported",
 		},
+		{
+			name:            "Median({1 '', 2 'g'})",
+			cql:             "Median({1 '', 2 'g'})",
+			wantErrContains: "Median(List<Quantity>) operand has different units which is not supported",
+		},
 	}
 
 	for _, tc := range tests {
@@ -694,7 +699,7 @@ func TestMedian_Error(t *testing.T) {
 			}
 
 			_, err = interpreter.Eval(context.Background(), parsedLibs, defaultInterpreterConfig(t, p))
-			if !strings.Contains(err.Error(), tc.wantErrContains) {
+			if err == nil || !strings.Contains(err.Error(), tc.wantErrContains) {
 				t.Errorf("Eval returned unexpected error: %v, want error containing %q", err, tc.wantErrContains)
 			}
 		})