Hello Zakaria,

In odoo v10 I check it, It works fine. Not getting the error.

As per your error, it generates when a variable value is got False or Null.

See the below example:
e.g:

x = "YOGENDRASINH"

x.lower()

Result : yogendrasinh

But,

x = False

x.lower()

it will raise an error.

AttributeError: 'bool' object has no attribute 'lower'

If you have any custom modules and installed then check the code first.

Thanks