SpringBoot NPE in RabbitProperties when user is given, but password not

private final RabbitProperties properties = new RabbitProperties();

    @Test
    void determineUsernameWithoutPassword() {
        this.properties.setAddresses("user@rabbit1.example.com:1234/alpha");
        assertThat(this.properties.determineUsername()).isEqualTo("user");
        assertThat(this.properties.determinePassword()).isEqualTo("guest");
    }

This throws an NPE:

java.lang.NullPointerException: Cannot load from object array because "split" is null

    at org.springframework.boot.autoconfigure.amqp.RabbitProperties$Address.parseUsernameAndPassword(RabbitProperties.java:1135)
    at org.springframework.boot.autoconfigure.amqp.RabbitProperties$Address.<init>(RabbitProperties.java:1112)
    at org.springframework.boot.autoconfigure.amqp.RabbitProperties.parseAddresses(RabbitProperties.java:223)
    at org.springframework.boot.autoconfigure.amqp.RabbitProperties.setAddresses(RabbitProperties.java:217)
    at org.springframework.boot.autoconfigure.amqp.RabbitPropertiesTests.determineUsernameWithoutPassword(RabbitPropertiesTests.java:233)
...

The code expects that username and password is given, only username doesn't work.