null 처리 추가

src/main/java/com/eactive/testmaster/server/mapper/ServerMapper.java

@@ -7,6 +7,7 @@ import com.eactive.testmaster.server.dto.ServerOptionDTO;
 import com.eactive.testmaster.server.entity.Server;
 import com.eactive.testmaster.server.entity.ServerOption;
 import com.eactive.testmaster.server.repository.ServerRepository;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
 import java.util.stream.Collectors;
@@ -76,14 +77,14 @@ public class ServerMapper {
     }
     public List<ServerOption> mapOptions(List<ServerOptionDTO> dtos) {
         if (dtos == null) {
-            return null;
+            return new ArrayList<>();
         }
         return dtos.stream().map(this::map).filter(Objects::nonNull).collect(Collectors.toList());
     }
 
     public List<ServerOptionDTO> mapOptionsDTO(List<ServerOption> entities) {
         if (entities == null) {
-            return null;
+            return new ArrayList<>();
         }
         return entities.stream().map(this::map).filter(Objects::nonNull).collect(Collectors.toList());
     }