BIDSLayout.get -- TypeError: unhashable type: 'list'

[oesteban]

Playing around metadata getters, and after working out a patch for the sibling issue #681, I've found the following related problem:

In [11]: l.get_suffixes()
Out[11]:
['bold',
 'description',
 'epi',
 'magnitude1',
 'participants',
 'phasediff',
 'sbref',
 'T1w']

In [12]: l.get_IntendedFor()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-12-9bcef017758c> in <module>
----> 1 l.get_IntendedFor()

~/workspace/pybids/bids/layout/layout.py in get(self, return_type, target, scope, regex_search, absolute_paths, invalid_filters, **filters)
    678
    679             if return_type == 'id':
--> 680                 results = list(set([x.entities[target] for x in results]))
    681                 results = natural_sort(results)
    682

TypeError: unhashable type: 'list'

In this case, the problem arises from the fact that lists are not hashable for the set, but some IntendedFor has a list inside.

[adelavega]

Just had this same issue pop up when trying to do get_tasks. Turn out a match for task was a description for said column in participants.json. Probably should exclude dicts/metadata from id type returns.