当[NSObject subscribe:on:]的第二个参数无意传入了的nil对象，下面的代码必崩；

[zhouxueyun]

QTEventBus/Sources/Core/NSObject+QTEventBus.m

Line 32 in f11966f

return bus.on(eventClass).freeWith(self);

[NSObject subscribeName:on:] 同理

QTEventBus/Sources/Core/NSObject+QTEventBus.m

Line 28 in f11966f

return bus.on(NSString.class).ofSubType(eventName).freeWith(self);