code: func (container *Container) InitDNSHostConfig() {
  	container.Lock()
  	defer container.Unlock()
  	if container.HostConfig.DNS == nil {
  		container.HostConfig.DNS = make([]string, 0)
  	}
  
  	if container.HostConfig.DNSSearch == nil {
  		container.HostConfig.DNSSearch = make([]string, 0)
  	}
  
  	if container.HostConfig.DNSOptions == nil {
  		container.HostConfig.DNSOptions = make([]string, 0)
  	}
  }
docs: // InitDNSHostConfig ensures that the dns fields are never nil.
  // New containers don't ever have those fields nil,
  // but pre created containers can still have those nil values.
  // The non-recommended host configuration in the start api can
  // make these fields nil again, this corrects that issue until
  // we remove that behavior for good.
  // See https://github.com/docker/docker/pull/17779
  // for a more detailed explanation on why we don't want that.