Error when processing resource files with null/empty annotations

[phanimarupaka]

Kpt reads KRM resources from files, adds annotations config.kubernetes.io/index and config.kubernetes.io/path, processes them and writes them back to respective file paths in original order. There is an edge case where kpt is not creating/adding annotations if the annotations field is already specified in resource files and is null/empty.

[phanimarupaka]

@pwittrock Why are we returning nil here instead of err. As this logic is used everywhere, nil fields are not being matched without explicit error which is leading to confusion. How should PathGetter behave if there are nil fields.

metadata:
     annotations:

For this yaml input with nil annotations, but field exists, kyaml doesn't add annotations.

cc @mortent