mandatory in field definition should be:
identifier, field type all other optional.
Currently wrong:
If no name is set then the field definition is not inserted in the db (corrupt)
If no fieldgroup is set the field definition is not shown in the legacy GUI
(this should be checked and fixed on server side)
If no fieldSetting is present on xml field type the server returns a 500
If no position is given, the server should generate it from the order of the field definitions (currently error 500)