(a isa A).output
(a isa Object).output
(not a isa B).output
-var c: Object = null
+(a isa nullable A).output
+(a isa nullable Object).output
+(not a isa nullable B).output
+var c: nullable Object = null
(c isa A).output
(c isa Object).output
(c isa B).output
+(c isa nullable A).output
+(c isa nullable Object).output
+(c isa nullable B).output