url: .search property is inconsistent depending on parseQueryString

[tniessen]

• Version: master
• Platform: Windows
• Subsystem: url

Parsing a URL without a search part changes its behavior if parseQueryString is set:

> url.parse('http://example.com/', false).search
null
> url.parse('http://example.com/', true).search
''

We should probably change this line

this.search = '';

to this

this.search = null;

Users most likely will not expect parseQueryString to affect the value of .search.

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There was a similar discussion at #9600, but @sam-github and I both think that the behavior discussed there is in fact justifiable.

Is there any justification for this behavior or do we consider this a bug? If we do, I will create a semver-major PR later. (I know that we do not plan to make any big changes to the old url API, but I would personally consider this a bug.)

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cc @nodejs/url