Add test for handling missing property

Fixes #854

Author: antonmedv

test/issues/854/issue_test.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/expr-lang/expr"
+	"github.com/expr-lang/expr/internal/testify/require"
+	"github.com/expr-lang/expr/types"
+)
+
+func TestIssue854(t *testing.T) {
+	envType := types.Map{
+		"user": types.Map{
+			// If we do not specify `Profile` here,
+			// this is a correct behavior to throw
+			// on a missing property.
+		},
+	}
+
+	code := `user.Profile?.Address ?? "Unknown address"`
+
+	_, err := expr.Compile(code, expr.Env(envType))
+	require.Error(t, err)
+}