Fix: https://github.com/rails/rails/issues/44452
We don't ignore blank path strings because as surprising as it is, they
are valid paths:
```ruby
>> path = Pathname.new(" ")
=> #<Pathname: >
>> path.write("test")
=> 4
>> path.exist?
=> true
```
Previously it would end up calling `Pathname#empty?` which returned true
if the path existed and was an empty directory or file.
That behavior was unlikely to be expected.
