ProviderManager#checkState() throws NullPointerException

[yukihane]

Describe the bug

When use java.util.List.of(), ProviderManager#checkState() throws NullPointerException.

checkState() uses List#contains(null) since #7713 (comment), but it may throws NullPointerException:

NullPointerException - if the specified element is null and this list does not permit null elements (optional)

To Reproduce

new ProviderManager(List.of(myProvider));

Expected behavior

NPE is not thrown.

[jzheaux]

@yukihane thank you for the suggestion that the exception be refined. It's a nice improvement to be able to replace an NPE with a more helpful error message.

Would you be interested in submitting a PR to change this check into a for loop?