Hiding nil values, understanding why golang fails here

I fail to understand how to correctly assure that something is not nil in this case:

package main

type shower interface {
  getWater() []shower

type display struct {
  SubDisplay *display

func (d display) getWater() []shower {
  return []shower{display{}, d.SubDisplay}

func main() {
  // SubDisplay will be initialized with null
  s := display{}
  // water := []shower{nil}
  water := s.getWater()
  for _, x := range water {
    if x == nil {
      panic("everything ok, nil found")

    //first iteration display{} is not nil and will
    //therefore work, on the second iteration
    //x is nil, and getWater panics.

The only way I found to check if that value is actually nil is by using reflection.

Is this really wanted behaviour? Or do I fail to see some major mistake in my code?

Play link here