Avoid parsing empty 6

[DanielCKennedy]

Cherry-pick of #618 and #621 to add to 0.6 release

What this PR does / why we need it:
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.

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 #

[k8s-ci-robot]

Hi @DanielCKennedy. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[nckturner]

/ok-to-test

[nckturner]

/test pull-aws-iam-authenticator-e2e

[nckturner]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: DanielCKennedy, nckturner

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