v5.2.2 upgrade to v5.3.0, found "[<unknown>] ["HTTPHandler: Code: 62, e.displayText() = DB::Exception: Empty query, e.what() = DB::Exception,"

using default config, from v5.2.2 upgrade to v5.3.0, found following error in log:

[<unknown>] ["HTTPHandler: Code: 62, e.displayText() = DB::Exception: Empty query, e.what() = DB::Exception, Stack trace:\n\n0. bin/tiflash/tiflash(StackTrace::StackTrace()+0x16) [0x3921fd6]\n
1. bin/tiflash/tiflash(DB::Exception::Exception(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int)+0x26) [0x3915e56]\n
2. bin/tiflash/tiflash(DB::parseQueryAndMovePosition(DB::IParser&, char const*&, char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool, unsigned long)+0x8e) [0x811799e]\n
3. bin/tiflash/tiflash(DB::parseQuery(DB::IParser&, char const*, char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned long)+0x1e) [0x8117a1e]\n
4. bin/tiflash/tiflash(DB::SQLQuerySource::parse[abi:cxx11](unsigned long)+0x5d) [0x7dca49d]\n
5. bin/tiflash/tiflash() [0x77a372e]\n
6. bin/tiflash/tiflash(DB::executeQuery(DB::ReadBuffer&, DB::WriteBuffer&, bool, DB::Context&, std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)>)+0x118) [0x77a4e48]\n
7. bin/tiflash/tiflash(DB::HTTPHandler::processQuery(Poco::Net::HTTPServerRequest&, HTMLForm&, Poco::Net::HTTPServerResponse&, DB::HTTPHandler::Output&)+0x350e) [0x398aade]\n
8. bin/tiflash/tiflash(DB::HTTPHandler::handleRequest(Poco::Net::HTTPServerRequest&, Poco::Net::HTTPServerResponse&)+0x3af) [0x398d01f]\n
9. bin/tiflash/tiflash(Poco::Net::HTTPServerConnection::run()+0x2fe) [0x83f5e5e]\n
10. bin/tiflash/tiflash(Poco::Net::TCPServerConnection::start()+0xf) [0x83eed3f]\n
11. bin/tiflash/tiflash(Poco::Net::TCPServerDispatcher::run()+0x166) [0x83ef106]\n
12. bin/tiflash/tiflash(Poco::PooledThread::run()+0x77) [0x8578267]\n
13. bin/tiflash/tiflash(Poco::ThreadImpl::runnableEntry(void*)+0x38) [0x8574118]\n
14. bin/tiflash/tiflash() [0x8e571bf]\n
15. /lib64/libpthread.so.0(+0x7ea5) [0x7f46f505bea5]\n
16. /lib64/libc.so.6(clone+0x6d) [0x7f46f4a829fd]\n"] [thread_id=8]

tiflash hash: 7f5b61e3dfb89b8f4172a7e0f37f1f7763b5d06e

Start by reproducing the v5.2.2-to-v5.3.0 upgrade with the default configuration and inspect the HTTPHandler::processQuery and SQLQuerySource::parse stack entries. Trace which request produces the empty query, then verify the behavior against the reported tiflash hash and add a regression check if the relevant test location is identified. Done means the empty-query error no longer occurs for the triggering request.