IllegalArgumentException in SslServerCustomizer.loadStore if ssl.getKeystore() returns null

[billore]

I have recently upgraded spring-boot from 2.0.8 to 2.1.4.
After upgrade, I have started seeing IllegalArgumentException in SslServerCustomizer.loadStore if ssl.getKeystore() returns null.

Looking at the code diff, in to older version(2.0.8) there was a null check for resource in the loadStore(), before calling into ResourceUtils.getURL(resource);

It looks like this null check is missing in the latest version and due to that, IllegalArgumentException is thrown at a later stage.
Due to this, my existing code has stopped working.

Caused by: java.lang.IllegalArgumentException: Resource location must not be null
	at org.springframework.util.Assert.notNull(Assert.java:198) ~[spring-core-5.1.6.RELEASE.jar!/:5.1.6.RELEASE]
	at org.springframework.util.ResourceUtils.getURL(ResourceUtils.java:130) ~[spring-core-5.1.6.RELEASE.jar!/:5.1.6.RELEASE]
	at org.springframework.boot.web.embedded.netty.SslServerCustomizer.loadStore(SslServerCustomizer.java:164) ~[spring-boot-2.1.4.RELEASE.jar!/:2.1.4.RELEASE]
	at org.springframework.boot.web.embedded.netty.SslServerCustomizer.loadKeyStore(SslServerCustomizer.java:147) ~[spring-boot-2.1.4.RELEASE.jar!/:2.1.4.RELEASE]
	at org.springframework.boot.web.embedded.netty.SslServerCustomizer.getKeyStore(SslServerCustomizer.java:117) ~[spring-boot-2.1.4.RELEASE.jar!/:2.1.4.RELEASE]
	at org.springframework.boot.web.embedded.netty.SslServerCustomizer.getKeyManagerFactory(SslServerCustomizer.java:96) ~[spring-boot-2.1.4.RELEASE.jar!/:2.1.4.RELEASE]

[snicoll]

Looks like the null check was kept for trust store but got removed for key store.

[wilkinsona]

This was intentional as it aligns Netty's behaviour with that of Jetty, Tomcat, and Undertow. See #15709 for the details.

@billore Can you please describe what you are trying to do? It may be that you were relying on a bug in which case your code may have to change or it may be that you have a use case that we haven't considered and we should change all 4 embedded containers that we support to accommodate it.

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