Settings hierarchy overrides empty values

[fzumstein]

If you have an xlwings.conf sheet with all settings in there, empty values get overridden if you have them specified further down in the hierarchy (e.g. in a user config file). For example:

sheet

Conda Path | (empty)

user config file

"Conda Path","C:\some\path" 

Will use C:\some\path instead of using the empty value as it should.