Fix the stub for layerActionForKey: to let CA continue the search (#1441)

* Fix the stub for layerActionForKey: to let CA continue the search

* Kick CI

Author: Adlai-Holler

Source/ASDisplayNode.mm

@@ -106,7 +106,10 @@ BOOL ASDisplayNodeNeedsSpecialPropertiesHandling(BOOL isSynchronous, BOOL isLaye
 void StubImplementationWithNoArgs(id receiver, SEL _cmd) {}
 void StubImplementationWithSizeRange(id receiver, SEL _cmd, ASSizeRange sr) {}
 void StubImplementationWithTwoInterfaceStates(id receiver, SEL _cmd, ASInterfaceState s0, ASInterfaceState s1) {}
-id StubLayerActionImplementation(id receiver, SEL _cmd, NSString *key) { return (id)kCFNull; }
+
+/// Returning nil here won't trigger unwanted default actions, because we override
+/// +defaultActionForKey: to return kCFNull.
+id StubLayerActionImplementation(id receiver, SEL _cmd, NSString *key) { return nil; }
 
 /**
  *  Returns ASDisplayNodeFlags for the given class/instance. instance MAY BE NIL.