refactor: 참가자 생성 가능 여부를 판단할 때 미팅의 maxParticipants가 null인 경우에 대한 예외처리 추가

controllers/participant.js

@@ -75,7 +75,10 @@ exports.createParticipant = async (req, res, next) => {
     const meeting = await getMeetingById(meetingId);
     const currentParticipants =
       await getNumOfParticipantsByMeetingId(meetingId);
-    if (currentParticipants >= meeting.maxParticipants) {
+    if (
+      meeting.maxParticipants &&
+      currentParticipants >= meeting.maxParticipants
+    ) {
       throw createMaxParticipantsError();
     }