I get this error when loading SVM, with a preset or no preset at all. Removing the mod fixes it and I don't know why. I have tried checking the spt server db folder for traders and nothing seems to give null.
I have Painter, Hephasteus as new traders
Re-save'n're-apply your preset, maybe the field went null or something, i've seen that error before but there was no straightforward solution, people just got it fixed eventually.