Where was it suggested that nulls are the biggest problem for developers?
But they are a problem that happens, and in Kotlin, the compiler checks your nullable logic for you; instead of your users finding the errors at runtime.
It was suggested that that feature is relevant enough to justify using kotlin over Java. However, I'd (and others in this very thread also have) argue that only slightly tips the scales towards Kotlin, while not solving the problem they were actually trying to solve here: reduce the barrier for contributing.
It just a way to conceal bad coding practices, which doesn’t prevent from having the same problem in a different form, just like GC in JVM cannot protect from all memory leaks. I can hardly remember a case when NPE was reported by some user in my projects.
But they are a problem that happens, and in Kotlin, the compiler checks your nullable logic for you; instead of your users finding the errors at runtime.