Error in marshalling can cause a TypeError

[robyoung]

Code

from flask_restx import Model, marshal, fields

model = Model('Test', {'field': fields.Float()})

marshal({'field': {'min': '12.1', 'max': '12.2'}}, model)

Expected Behavior

Given the example code I would expect to receive a MarshallingError with a useful error message directing me to where the problem is.

Actual Behavior

I receive a TypeError only telling me the underlying error with no context.

Environment

• Python version: 3.8
• Flask version: 1.1.1
• Flask-RESTX version: 0.1.1

Additional Context

I have a PR incoming for this. I am opening this issue as that is what the CONTRIBUTING guidelines suggest.