Fix options can be undefined instead of having a default value

[awesometic]

Hi, thanks for creating this useful library.

In my usage, mostly on NestJS, I think it can't do what it should do in recognizing parent folders. I don't know exactly why it happens in my environment, since this looks like a quite big issue if it doesn't work on every workspace.

Please review this patch. :) Below is the description of this commit I wrote.

edit) I just realize that this issue is already reported. It can fix issue #9 , which is the exactly same as mine.

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When an import is something like the below,

import something from '../../some/folder';

Currently this plugin cannot fix that to be like,

import something from 'src/some/folder';

This because the rootDir variable in the isParentFolder function is treated as undefined unless a user set that variable by its option.

So that patch will fix this that rootDir not to be undefined, rather it makes that an empty string by setting a default value.

In the case of allowSameFolder, undefined will be treated as false so it has been doing as it should be.

Signed-off-by: Deokgyu Yang secugyu@gmail.com