./outputs/BX992_all_1 not found
./outputs/BX992_all_1_summary not found
Traceback (most recent call last):
  File "/home/russ/Documents/projects/gnss-diff/env_diff/bin/diff_cno", line 33, in <module>
    sys.exit(load_entry_point('gnss-diff', 'console_scripts', 'diff_cno')())
  File "/home/russ/Documents/projects/gnss-diff/diff_cno.py", line 397, in main
    sv_types_ref = df_ref.SVType.unique()
AttributeError: 'NoneType' object has no attribute 'SVType'