Create Dataset: Form validation not working on save, throws stack trace, gray screen

[kcondon]

This works in 4.20, doesn't work in current dev.
Some code investigation (thanks jim) indicates it likely changed here: #6909

Steps to reproduce:

1. create dataset, delete host dv, enter title, leaving rest of required fields empty, save
2. notice null ptr errors in server log, UI has gray overlay on dataset form, no validation errors. in 4.20 on demo, throws normal missing entry validation errors.