TypeError: unsupported operand type(s) for +: 'Nonetype' and 'list'

I am facing this issue while using 'bench init frappe-bench'.
I have downloaded it using 'pip3 install frappe-bench'
I found this issue closed but no solution has seemed to work.

/usr/local/Cellar/python/3.7.6_1/bin/python3.7: Error while finding module specification for 'frappe.utils.bench_helper' (ModuleNotFoundError: No module named 'frappe')

Traceback (most recent call last):
File "/usr/local/bin/bench", line 11, in
load_entry_point('frappe-bench', 'console_scripts', 'bench')()
File "/Users/narendra/Development/bench-repo/bench/cli.py", line 48, in cli
if sys.argv[1] in get_frappe_commands() + ["--site", "--verbose", "--force", "--profile"]:
TypeError: unsupported operand type(s) for +: 'NoneType' and 'list'

Start with bench/cli.py at the cli entry point and inspect how get_frappe_commands() is used in the failing command check. Reproduce the bench init invocation in the reported Python environment and trace why the command list is unavailable. Done means the reported TypeError and related module-loading failure are understood and covered by an appropriate verification.

Written by the indexing model from the issue text.