BUG. Custom additional fields on WI card. Board crashes on some fields.

Hi!
I think it's better to discuss here, rather then at VS Marketplace.
As I published as VSM I tried to add custom field from another extension (our own development):
```javascript
{ "fields":[ { "name":"Logrocon.PerformerIT", "title":"Developer" } ] }
```
it has same type as AssignedTo. And it crashed the board:

But when I add string field from same extension:
```javascript
{ "fields":[ { "name":"Logrocon.CustomerContact.1C", "title":"Contact" } ] }
```
everything goes normal: