slugify returns None when input is in string.ascii_letters

[karmux]

slugify('Slugify Me') returns None unexpectedly instead of slugify-me. language_code is not detected.

slugify('Slufigy Müõöä') returns slufigy-mueaoeae as expected. language_code is detected as l1.

[egorgvo]

I have bypassed this issue by adding an insignificant letter in a different language. More specifically, I am adding Russian 'ъ':
slugify('ъSlugify Me') will return slugify-me