Revert 'asNode(null)' to 'asNode()'.

[kevinlind]

Using 'asNode()' gives warning about implicit null value, however passing 'asNode(null)' fails to build publish step.

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #87 (0d7d2a8) into dev-v2.3.0 (5d322f8) will not change coverage.
The diff coverage is n/a.

@@              Coverage Diff              @@
##             dev-v2.3.0      #87   +/-   ##
=============================================
  Coverage         83.84%   83.84%           
  Complexity          385      385           
=============================================
  Files                29       29           
  Lines              1578     1578           
  Branches            223      223           
=============================================
  Hits               1323     1323           
  Misses              161      161           
  Partials             94       94           

Flag	Coverage Δ
functional-tests	66.48% <ø> (ø)
unit-tests	79.78% <ø> (ø)

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