Fix: relative imports from '' package are not allowed

[podtserkovskiy]

Summary

When we resolve a relative import from root package "", we get the import prefixed by "."
However, this kind of imports are not allowed and cpython throws an error:

/Users/michaelpo/PycharmProjects/pythonProject/venv/bin/python /Users/michaelpo/PycharmProjects/pythonProject/main.py 
Traceback (most recent call last):
  File "/Users/michaelpo/PycharmProjects/pythonProject/main.py", line 2, in <module>
    from .l1 import l1_func
ImportError: attempted relative import with no known parent package

Process finished with exit code 1

Test Plan

Unit tests

[amyreese]

thank you!