refactor(merge,split,json): adopt streaming approach and standardize types, address gradle warnings (#5803)

Co-authored-by: Anthony Stirling <[email protected]>
Co-authored-by: Balázs <[email protected]>

app/core/src/main/resources/application.properties

@@ -1,4 +1,9 @@
 multipart.enabled=true
+
+# Jackson 3 defaults FAIL_ON_NULL_FOR_PRIMITIVES to true (was false in Jackson 2).
+# Restore Jackson 2 behaviour so absent/null JSON fields map to Java primitive defaults.
+spring.jackson.deserialization.fail-on-null-for-primitives=false
+
 logging.level.org.springframework=WARN
 logging.level.org.springframework.security=WARN
 logging.level.org.hibernate=WARN
@@ -25,14 +30,16 @@ server.compression.enabled=true
 server.compression.min-response-size=1024
 server.compression.mime-types=application/json,application/xml,text/html,text/plain,text/css,application/javascript
 
-server.error.path=/error
-server.error.whitelabel.enabled=false
-server.error.include-stacktrace=always
-server.error.include-exception=true
-server.error.include-message=always
+spring.web.error.path=/error
+spring.web.error.whitelabel.enabled=false
+spring.web.error.include-stacktrace=always
+spring.web.error.include-exception=true
+spring.web.error.include-message=always
 
-# Enable RFC 7807 Problem Details for HTTP APIs
-spring.mvc.problemdetails.enabled=true
+# Disable Spring's built-in ProblemDetailsExceptionHandler (@Order(0)) so that
+# GlobalExceptionHandler runs first and provides detailed, logged error responses.
+# GlobalExceptionHandler already produces RFC 7807 ProblemDetail objects.
+spring.mvc.problemdetails.enabled=false
 
 #logging.level.org.springframework.web=DEBUG
 #logging.level.org.springframework=DEBUG