code: func (body Body) MarshalJSON() ([]byte, error) {
  	// Serialize empty Body to empty array. This handles both the empty case and the
  	// nil case (whereas by default the result would be null if body was nil.)
  	if len(body) == 0 {
  		return []byte(`[]`), nil
  	}
  	return json.Marshal([]*Expr(body))
  }
docs: // MarshalJSON returns JSON encoded bytes representing body.