create_cache returns None, results in IORegistryError

Sentry Issue: GWCELERY-TK

IORegistryError: Format could not be identified based on the file name or contents, please provide a 'format' argument.
The available formats are:
   Format    Read Write Auto-identify
------------ ---- ----- -------------
         csv  Yes   Yes           Yes
         gwf  Yes   Yes           Yes
gwf.framecpp  Yes   Yes            No
gwf.lalframe  Yes   Yes            No
        hdf5  Yes   Yes           Yes
   hdf5.losc  Yes    No            No
         txt  Yes   Yes           Yes
         wav  Yes   Yes           Yes
(1 additional frame(s) were not displayed)
...
  File "gwpy/timeseries/core.py", line 314, in read
    return timeseries_reader(cls, source, *args, **kwargs)
  File "gwpy/timeseries/io/core.py", line 50, in read
    return io_read_multi(joiner, cls, source, *args, **kwargs)
  File "gwpy/io/mp.py", line 79, in read_multi
    kwargs['format'] = get_read_format(cls, path, (source,) + args, kwargs)
  File "gwpy/io/registry.py", line 95, in get_read_format
    return get_format('read', cls, filepath, fileobj, args, kwargs)
  File "astropy/io/registry.py", line 603, in _get_valid_format
    "{}".format(format_table_str))