Path error with geteventhist

[mhearne-usgs]

Describe the bug
geteventhist us70006vll -p origin --split
Traceback (most recent call last):
File "/Users/mhearne/miniconda/envs/comcat/bin/geteventhist", line 11, in
load_entry_point('libcomcat', 'console_scripts', 'geteventhist')()
File "/Users/mhearne/src/python/libcomcat/libcomcat/bin/geteventhist.py", line 427, in main
pframe, product=product)
File "/Users/mhearne/src/python/libcomcat/libcomcat/bin/geteventhist.py", line 263, in save_dataframe
event.id + '_' + product + '.csv')
File "/Users/mhearne/miniconda/envs/comcat/lib/python3.7/posixpath.py", line 80, in join
a = os.fspath(a)
TypeError: expected str, bytes or os.PathLike object, not NoneType