Double null coordinates for Kerr-Newman-de Sitter spacetimes

We construct double null coordinates for subextremal Kerr-Newman-de Sitter spacetimes. This was already done for Kerr spacetimes by Pretorius and Israel and by Dafermos and Luk. These coordinates allow one to immediately extend some results previously proven for Kerr. As an example, we illustrate how Sbierski's result, for the wave equation on the black hole interior, for Reissner-Nordstr\"{o}m and Kerr spacetimes, applies to Kerr-Newman-de Sitter spacetimes.