base_isa_nullable2.nit:27,8--23: Warning: Expression is already a nullable A since it is a A.
base_isa_nullable2.nit:29,8--30: Warning: Expression is already a nullable B[Object] since it is a B[Object].
base_isa_nullable2.nit:30,8--39: Warning: Expression is already a nullable B[nullable Object] since it is a nullable B[Object].
base_isa_nullable2.nit:33,8--30: Warning: Expression is already a C[nullable Object].
true