Objective-c send messages to nil

In objective-c, sending messages to nil is not crash.

The reason is that when the execution ID objc_msgsend (id self, SEL op, ...) method, if self = nil, the function does not perform any meaningful action and returns directly.

The return value of the message sent to the nil object depends on the return type of the method:

Returns nil if the method's return value is an object pointer.

If the return value of the method is a pointer to a normal data type, NULL is returned.

Returns 0 if the return value of the method is integral and floating-point.