Avoid parsing known empty inputs

[dims]

We are seeing instances of the configmap in the wild with variations like below:

apiVersion: v1
data:
mapAccounts: |
    ''
mapUsers: |
    ""

We should tolerate these as the user literally means, there's no data they need in there.

What this PR does / why we need it:

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

[ivelichkovich]

We should backport this into v0.5.X

[divyasri537]

lgtm

[k8s-ci-robot]

@divyasri537: changing LGTM is restricted to collaborators

In response to this:

/lgtm

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[nnmin-aws]

/lgtm

[nnmin-aws]

/approve

[nnmin-aws]

/lgtm -i

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

Approval requirements bypassed by manually added approval.

This pull-request has been approved by: dims, nnmin-aws

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[nnmin-aws]

/merge