If ConnectionError is raised from requests boom failed on weird traceback

If ConnectionError is raised from requests boom failed on 

    -------- Results --------
    Successful calls        0
    Traceback (most recent call last):
      File "_boom.py", line 273, in <module>
        main()
      File "_boom.py", line 268, in main
        print_stats()
      File "_boom.py", line 56, in print_stats
        print('Total time       \t\t%.4f s' % _total)
    TypeError: float argument required, not NoneType