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To statically analyze whether you receive an empty collection or not, you need dependent types, a thing which Java does not have, and will not have in foreseeable future.

To tell mutable and immutable collections apart, you just need two separate interfaces, a feature available in Java for decades, and an approach widely and routinely used everywhere in the language.

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> To tell mutable and immutable collections apart, you just need two separate interfaces, a feature available in Java for decades, and an approach widely and routinely used everywhere in the language.

Part of the problem might be that Java's existing interfaces for collections don't have that split. `List`, `Set`, and `Map` already declare mutators, and they're used pervasively.

On the other hand, the Java folks clearly recognize that mutability is the wrong default for modern programming languages, so why double down on the mistakes of the past? They might argue that it makes more sense to follow established patterns than it does to create new ones, because it creates less friction for Java developers.

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