workflows: process arxiv math workflow update

Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>
Confirmed:
```python
In [2]: b = BibWorkflowObject.query.get(None)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-2-49243b10afc8> in <module>()
----> 1 b = BibWorkflowObject.query.get(None)

/home/jlavik/envs/labs/local/lib/python2.7/site-packages/sqlalchemy/orm/query.pyc in get(self, ident)
    816         mapper = self._only_full_mapper_zero("get")
    817 
--> 818         if len(ident) != len(mapper.primary_key):
    819             raise sa_exc.InvalidRequestError(
    820                 "Incorrect number of values in identifier to formulate "

TypeError: object of type 'NoneType' has no len()
```