fix(jsonpath): return a null object member instead of skipping it on-demand

include/sonic/internal/arch/simd_skip.h

@@ -959,15 +959,21 @@ class SkipScanner2 {
       }
 
       if (found) {
-        // if not null
-        if (peek() != 'n') {
-          return getJsonPath<style, serializeFlags>(
-              path, index + 1, jsonGenerator, jsonGeneratorFactory);
-        } else {
+        // A null value only has to be skipped when the path continues past it,
+        // because nothing can be selected out of null. When the key is the last
+        // step, null is the result the caller asked for, so recurse and let the
+        // path_is_nil branch emit it -- exactly what the array element path
+        // already does for e.g. "$[0]" over "[null]".
+        // Under FLATTEN/QUOTE this call is collecting wildcard results, where
+        // nulls are deliberately dropped (see JsonPath.WildcardFiltersNull),
+        // so the skip must stay unconditional there.
+        if (peek() == 'n' && (style != RAW || index + 1 < path.size())) {
           // skip null
           RETURN_FALSE_IF_PARSE_ERROR(skipOne());
           return false;
         }
+        return getJsonPath<style, serializeFlags>(
+            path, index + 1, jsonGenerator, jsonGeneratorFactory);
       }
       return false;
     }

tests/jsonpath_test.cpp

@@ -415,7 +415,8 @@ TEST(JsonPath, BadCases) {
 TEST(JsonPath, KeyNullElementPair) {
   auto json =
       R"( { "last_name": "Kim", "first_name":"Sam", "gender": false, "income": null, "age": 38} )";
-  TestOk(json, "$.income", "");
+  TestOk(json, "$.income",
+         "null");  // null object member returned, not skipped (aligns with DOM)
 }
 
 TEST(JsonPath, KeyIntoStringValue) {
@@ -767,6 +768,53 @@ TEST(JsonPathDom, NotFoundAndUnsupportedPath) {
   EXPECT_EQ(std::get<0>(unsupported), "");
 }
 
+TEST(JsonPathOnDemand, NullObjectMemberIsReturnedNotSkipped) {
+  // A null object member is a value, not a missing member. The on-demand
+  // backend skipped it whenever a key matched, so $.a over {"a":null} reported
+  // no match while the DOM backend returned "null" for the same input.
+  // The null only has to be skipped when the path continues past it, since
+  // nothing can be selected out of null.
+  struct Case {
+    const char* json;
+    const char* path;
+  };
+  for (const auto& c :
+       {Case{R"({"a":null})", "$.a"}, Case{R"({"a":null,"b":1})", "$.a"},
+        Case{R"({"b":1,"a":null})", "$.a"},
+        Case{R"({"a":{"b":null}})", "$.a.b"},
+        Case{R"({"a":[{"b":null}]})", "$.a[0].b"}}) {
+    auto od = GetByJsonPathOnDemand<kSerializeJavaStyleFlag>(c.json, c.path);
+    EXPECT_EQ(std::get<1>(od), kErrorNone) << c.json << " " << c.path;
+    EXPECT_EQ(std::get<0>(od), "null") << c.json << " " << c.path;
+    // Both backends must agree.
+    auto dom = GetByJsonPath(c.json, c.path);
+    EXPECT_EQ(std::get<1>(dom), std::get<1>(od)) << c.json << " " << c.path;
+    EXPECT_EQ(std::get<0>(dom), std::get<0>(od)) << c.json << " " << c.path;
+  }
+
+  // Arrays already behaved correctly; keep them covered so the two stay
+  // aligned.
+  for (const auto& c : {Case{"[null]", "$[0]"}, Case{"[1,null]", "$[1]"}}) {
+    auto od = GetByJsonPathOnDemand<kSerializeJavaStyleFlag>(c.json, c.path);
+    EXPECT_EQ(std::get<1>(od), kErrorNone) << c.json << " " << c.path;
+    EXPECT_EQ(std::get<0>(od), "null") << c.json << " " << c.path;
+  }
+
+  // The path continuing past a null must still not match.
+  for (const auto& c :
+       {Case{R"({"a":null})", "$.a.b"}, Case{R"({"a":null})", "$.a[0]"},
+        Case{R"({"a":{"b":null}})", "$.a.b.c"}}) {
+    auto od = GetByJsonPathOnDemand<kSerializeJavaStyleFlag>(c.json, c.path);
+    EXPECT_NE(std::get<1>(od), kErrorNone) << c.json << " " << c.path;
+  }
+
+  // Wildcard collection deliberately drops nulls; that must not change.
+  auto wc = GetByJsonPathOnDemand<kSerializeJavaStyleFlag>(
+      R"({"root": [{"a":null},{"a":"foo"},{"a":"bar"}]})", "$.root[*].a");
+  EXPECT_EQ(std::get<1>(wc), kErrorNone);
+  EXPECT_EQ(std::get<0>(wc), R"(["foo","bar"])");
+}
+
 TEST(JsonPathDom, NegativeIndexSupportedButOnDemandUnsupported) {
   auto dom_got = GetByJsonPath("[0,1,2]", "$[-1]");
   EXPECT_EQ(std::get<1>(dom_got), kErrorNone);