My colleague Sorin Basca reports:

A DESCRIPTION OF THE PROBLEM:

Calling Map.of().clear() results in an UnsupportedOperationException. However, calling Map.of().entrySet().clear() just returns doing nothing. Both calls should behave in the same way.

ROOT CAUSE:

Calling Map.of() returns an ImmutableCollections.EMPTY_MAP which returns a MapN object. MapN.entrySet() returns an object that does not override clear(), which means the default clear is used - it iterates and removes items until iterator.hasNext() is false - so the function just returns without removing anything. However, if calling MapN.clear() directly, this will throw an UnsupportedOperationException.

POSSIBLE SOLUTION:

Override clear() inside the entrySet class returned from MapN to also throw UnsupportedOperationException.