fix(clouddriver): NPE applying empty artifact manifest

[sepulvedablanco]

When a Deploy (Manifest) step is executed configuring an artifact without content, a java.lang.NullPointerException is thrown, which is displayed in Deck and the step fails as can be seen in the following screenshot:

[spinnakerbot]

The following commits need their title changed:

• 6e2bba6: Fix NPE while applying empty manifest

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<type>(<scope>): <subject>, e.g. fix(kubernetes): address NPE in status check

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[german-muzquiz]

Thanks for contributing!
Can you add a unit test validating that the issue that you were seeing is fixed? I assume that's by supplying a description with null values for both getManifests and getManifest. Also we need a test that uses the singular version because now all of them use only the plural version.

[german-muzquiz]

If both description.getManifests() and description.getManifest() return null, there will be a new NullPointerException in line 186, so we need to make sure that inputManifests is never null.