This bug results from DreamFactory schema editor requiring at least one field to be given in the request, even though MongoDB doesn't have defined fields.
Until the bug is resolved, you can work around this by doing something like this
The dummyfield will not actually be created, but it's necessary to get past the schema validation check.
This bug is being resolved in the current sprint (which started this week.) Sprints are typically 6 weeks long, so look for this fix ~ August 19