Description of problem:
When using `oc adm group sync` into a YAML file. The tool generates an empty item to the YAML file that prevents successful parsing later on. The `ac apply -f` does not work properly with this data and ends with non 0 return code.

Version-Release number of selected component (if applicable):
    4.8.13

How reproducible:
    100%

Steps to Reproduce:
    1. oc adm groups sync my_ldap_group --sync-config=sync-config.yaml -o yaml

Actual results:
    apiVersion: user.openshift.io/v1
    items:
    - metadata:
        creationTimestamp: null
      users: null
    - apiVersion: user.openshift.io/v1
      kind: Group
      metadata:
        annotations:
          openshift.io/ldap.sync-time: ...
          openshift.io/ldap.uid: ...

Expected results:
    Missing the first item that contains only null values.

Additional info:
    I believe that this was introduced with Bug 1936904