NullPointerException in SimpleAmqpHeaderMapper when message priority is null

[daniloarcidiacono]

In what version(s) of Spring AMQP are you seeing this issue?

4.0.0

Describe the bug

I encountered a NullPointerException in SimpleAmqpHeaderMapper when receiving messages that do not have the priority property explicitly set (i.e., when priority is null). This appears to be a regression in 4.0.0.

The stack trace points to an unboxing issue during header mapping:

java.lang.NullPointerException: Cannot invoke "java.lang.Integer.intValue()" because "priority" is null
	at org.springframework.amqp.support.SimpleAmqpHeaderMapper.toHeaders(SimpleAmqpHeaderMapper.java:155) ~[spring-amqp-4.0.0.jar:4.0.0]
	at org.springframework.amqp.support.SimpleAmqpHeaderMapper.toHeaders(SimpleAmqpHeaderMapper.java:57) ~[spring-amqp-4.0.0.jar:4.0.0]

Looking at the source for SimpleAmqpHeaderMapper.java (around line 155), the code attempts to compare a nullable Integer to a primitive int:

Integer priority = amqpMessageProperties.getPriority(); // Returns null if not set

// The condition (priority > 0) causes implicit unboxing of null, throwing NPE
javaUtils.acceptIfCondition(priority > 0, AmqpMessageHeaderAccessor.PRIORITY, priority, putObject)
         .acceptIfNotNull(...)

Comparison with previous versions:
In spring-amqp:2.4.3, this logic was null-safe:

Integer priority = amqpMessageProperties.getPriority();
javaUtils.acceptIfCondition(priority != null && priority > 0, ...);

In 4.0.0, the null check was removed, leading to the regression:

Integer priority = amqpMessageProperties.getPriority();
javaUtils.acceptIfCondition(priority > 0, ...); // NPE if priority is null

To Reproduce

1. Create a Spring Boot 4 application with spring-boot-starter-amqp.
2. Define a standard @RabbitListener.
3. Publish a message to the queue using RabbitTemplate (or the Management UI) without setting a specific priority property (leaving it as the default/null).
4. The listener container logs an exception and fails to process the message.

Expected behavior

The application should consume the message without error, treating the missing priority as null or 0, consistent with previous versions of Spring AMQP. It should not attempt to unbox a null Integer.

[artembilan]

I think RabbitTemplate.send(Message message) is not correct sample here to reproduce.
You cannot create a Message with default MessageProperties without priority: it comes as 0 over there by default.
But Management UI indeed leads to that NPE.
Sorry, about that: will be fixed soon.
The 4.0.1 is scheduled for December 15th.