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Issue details

When setting a CALayer delegate and using "actionForLayer:forKey:", NSNull is a valid and central return option. (See https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/CoreAnimation_guide/ReactingtoLayerChanges/ReactingtoLayerChanges.html)
However the roboVM binding for NSNull doesn't implement the CAAction interface.

Therefor NSNull can't be returned in the delegate. I also haven't found any cast methods to cast it natively, but maybe I have just missed them.

For reference, the MOE bindings of NSNull implement CAAction along with another interface:
https://github.com/multi-os-engine/moe-core/blob/dbe4cb4e6f69ecc5e5ea8b984532b8432a8ebb9e/moe.apple/moe.platform.ios/src/main/java/apple/foundation/NSNull.java#L47

Configuration

Versions:

• Robovm: 2.3.16