server(bug): fix json mget crash on invalid path (#4940)

* server: fix json mget crash on invalid path

---------

Signed-off-by: adi_holden <[email protected]>

Author: adiholden

src/server/json_family.cc

@@ -1269,6 +1269,8 @@ std::vector<std::optional<std::string>> OpJsonMGet(const WrappedJsonPath& json_p
           json_val, std::move(cb), CallbackResultOptions::DefaultEvaluateOptions());
 
       if (eval_result.IsV1()) {
+        if (eval_result.Empty())
+          return nullopt;
         return eval_result.AsV1();
       }
 

src/server/json_family_test.cc

@@ -4,6 +4,7 @@
 
 #include "server/json_family.h"
 
+#include <absl/flags/flag.h>
 #include <absl/strings/str_replace.h>
 
 #include "base/gtest.h"
@@ -16,6 +17,8 @@ using namespace testing;
 using namespace std;
 using namespace util;
 
+ABSL_DECLARE_FLAG(bool, jsonpathv2);
+
 namespace dfly {
 
 class JsonFamilyTest : public BaseFamilyTest {
@@ -2547,6 +2550,14 @@ TEST_F(JsonFamilyTest, MGetLegacy) {
   ASSERT_EQ(RespExpr::ARRAY, resp.type);
   EXPECT_THAT(resp.GetVec(), ElementsAre(R"("Israel")", R"("Germany")", ArgType(RespExpr::NIL)));
 
+  resp = Run({"JSON.MGET", "json1", "json2", ".[0]"});
+  if (auto jsonpathv2 = absl::GetFlag(FLAGS_jsonpathv2); jsonpathv2) {
+    ASSERT_EQ(RespExpr::ARRAY, resp.type);
+    EXPECT_THAT(resp.GetVec(), ElementsAre(ArgType(RespExpr::NIL), ArgType(RespExpr::NIL)));
+  } else {
+    EXPECT_THAT(resp, ErrArg("ERR syntax error"));
+  }
+
   resp = Run({"JSON.SET", "json3", ".", json[2]});
   ASSERT_THAT(resp, "OK");