I have defined following circular model in my API:

tree_model = api.model('TreeModel', {
    'node': fields.Nested(node_model)
})
tree['children'] = fields.List(fields.Nested(tree_model), default=[])

Marshalling such model with api.marshal_with works ok, but app crashes when I try to open swagger documentation:

RecursionError: maximum recursion depth exceeded
Fatal Python error: Cannot recover from stack overflow.

Current thread 0x00007f8731cf2700 (most recent call first):
File "/home/karol/App/pycharm-2016.2/helpers/pydev/_pydevd_bundle/pydevd_trace_dispatch_regular.py", line 139 in call
File "/home/karol/test-api/venv/lib/python3.5/site-packages/werkzeug/utils.py", line 68 in get
File "/home/karol/test-api/venv/lib/python3.5/site-packages/flask_restplus/fields.py", line 207 in nested
File "/home/karol/test-api/venv/lib/python3.5/site-packages/flask_restplus/swagger.py", line 468 in register_field
File "/home/karol/test-api/venv/lib/python3.5/site-packages/flask_restplus/swagger.py", line 460 in register_model
File "/home/karol/test-api/venv/lib/python3.5/site-packages/flask_restplus/swagger.py", line 468 in register_field
File "/home/karol/test-api/venv/lib/python3.5/site-packages/flask_restplus/swagger.py", line 470 in register_field
File "/home/karol/test-api/venv/lib/python3.5/site-packages/flask_restplus/swagger.py", line 460 in register_model
File "/home/karol/test-api/venv/lib/python3.5/site-packages/flask_restplus/swagger.py", line 468 in register_field
File "/home/karol/test-api/venv/lib/python3.5/site-packages/flask_restplus/swagger.py", line 470 in register_field
...

Process finished with exit code 134 (interrupted by signal 6: SIGABRT)

Swagger 2.0 accepts circular (recursive) models, so I think this library should handle such cases.
Quick fix could be to just check if model is already registered in Swagger.register_model method.

I am using 0.9.2 version