Nud Material XML Exporting/Importing exception

Exporting an xml from the "old" nud and applying it to the "new" nud with the below error:


Saving the nud seems to show that only about half the materials were properly applied.

[test.zip](https://github.com/jam1garner/Smash-Forge/files/2520552/test.zip)

Start with the XML export/import path described in the issue and reproduce the failure by applying an export from the old nud to the new nud. Use test.zip as the supplied fixture and inspect the exception shown in the linked image. Done means the import completes without an exception and saving applies all materials rather than only about half.

Written by the indexing model from the issue text.