Added Null and IsNull to eventually replace Empty

[dennisdoomen]

This pull request introduces a new "null" path concept to the ChainablePath API, replacing the previous use of the "empty" path for scenarios where a path does not exist or a search yields no results. The main changes include adding the Null static property, the IsNull property, and updating tests and API verification files to use and recognize these new members.

[coveralls]

Pull Request Test Coverage Report for Build 16901387721

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 96.341%

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Totals
Change from base Build 16901276436:	0.03%
Covered Lines:	172
Relevant Lines:	180

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💛 - Coveralls