biggestDump is an open source tool to dump your current and pending firmware from your Switch's NAND to use with ChoiDujourNX. Simply boot biggestDump, press A, and wait about 2 minutes for it to finish dumping the files. Open "sdmc:/Update/" in ChoiDujourNX and you're done. Any issues can be reported here or at Github. Testers and I have had no issues, but there is only so much we can test ourselves.
https://github.com/J-D-K/biggestDump
https://github.com/J-D-K/biggestDump