message: HOTFIX - only replace x-fwd-for if present
diff: rewrite_by_lua_block {
  local xff = {}
  + if ngx.var.http_x_forwarded_for then
  for ip in string.gmatch(ngx.var.http_x_forwarded_for, '([^,]+)') do
  if string.find(ip, "^::ffff:") then
  table.insert(xff,string.match(ip, "^::ffff:(.*)"))
  @@ -8,4 +9,5 @@ rewrite_by_lua_block {
  end
  ngx.req.set_header("X-Forwarded-For", table.concat(xff, ","))
  end
  + end
  }
  