grpc_arg_stack_pop_arg - Gets an argument from the stack.
  void *grpc_arg_stack_pop_arg(grpc_arg_stack_t *stack)
  grpc_arg_stack_t *stackThe grpc_arg_stack_pop_arg() function gets one argument pointer stored in the stack and returns it.
This function is MT-safe.
If successful, a pointer to an argument is returned. If failed, NULL is returned.
  GRPC_NOT_INITIALIZED  GRPC_OTHER_ERROR_CODE