Add an assertion to Person_print

lcthw/ex16.c

@@ -33,6 +33,8 @@ void Person_destroy(struct Person *who)
 
 void Person_print(struct Person *who)
 {
+	assert(who != NULL);
+
 	printf("Name: %s\n", who->name);
 	printf("\tAge: %d\n", who->age);
 	printf("\tHeight: %d\n", who->height);