BrainObservatoryCache.get_cell_specimens filter argument does not properly handle empty list

[dyf]

from allensdk.core.brain_observatory_cache import BrainObservatoryCache
boc = BrainObservatoryCache()
boc.get_cell_specimens(filters=[])

This should do something rational (like return all cells).

Instead I get this:

In [6]: boc.get_cell_specimens(filters=[])
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-6-4646ba69734a> in <module>()
----> 1 boc.get_cell_specimens(filters=[])

/local1/git/allensdk/allensdk/core/brain_observatory_cache.pyc in get_cell_specimens(self, fi                                                                        le_name, ids, experiment_container_ids, include_failed, simple, filters)
    409                                                         experiment_container_ids=expe                                                                        riment_container_ids,
    410                                                         include_failed=include_failed                                                                        ,
--> 411                                                         filters=filters)
    412
    413         # drop the thumbnail columns

/local1/git/allensdk/allensdk/api/queries/brain_observatory_api.pyc in filter_cell_specimens(                                                                        self, cell_specimens, ids, experiment_container_ids, include_failed, filters)
    566             cell_specimens = self.dataframe_query(cell_specimens,
    567                                                   filters,
--> 568                                                   'cell_specimen_id')
    569
    570         return cell_specimens

/local1/git/allensdk/allensdk/api/queries/brain_observatory_api.pyc in dataframe_query(self,                                                                         data, filters, primary_key)
    625         queries = self.dataframe_query_string(filters)
    626         result_dataframe = pd.DataFrame(data)
--> 627         result_dataframe = result_dataframe.query(queries)
    628
    629         result_keys = set(result_dataframe[primary_key])

/local1/anaconda3/envs/py2/lib/python2.7/site-packages/pandas/core/frame.pyc in query(self, e                                                                        xpr, inplace, **kwargs)
   2295         kwargs['level'] = kwargs.pop('level', 0) + 1
   2296         kwargs['target'] = None
-> 2297         res = self.eval(expr, **kwargs)
   2298
   2299         try:

/local1/anaconda3/envs/py2/lib/python2.7/site-packages/pandas/core/frame.pyc in eval(self, ex                                                                        pr, inplace, **kwargs)
   2364             kwargs['target'] = self
   2365         kwargs['resolvers'] = kwargs.get('resolvers', ()) + tuple(resolvers)
-> 2366         return _eval(expr, inplace=inplace, **kwargs)
   2367
   2368     def select_dtypes(self, include=None, exclude=None):

/local1/anaconda3/envs/py2/lib/python2.7/site-packages/pandas/core/computation/eval.pyc in ev                                                                        al(expr, parser, engine, truediv, local_dict, global_dict, resolvers, level, target, inplace)
    261
    262     if isinstance(expr, string_types):
--> 263         _check_expression(expr)
    264         exprs = [e.strip() for e in expr.splitlines() if e.strip() != '']
    265     else:

/local1/anaconda3/envs/py2/lib/python2.7/site-packages/pandas/core/computation/eval.pyc in _c                                                                        heck_expression(expr)
     99     """
    100     if not expr:
--> 101         raise ValueError("expr cannot be an empty string")
    102
    103

ValueError: expr cannot be an empty string