ObjectMeta has fields with omitempty json tags. This means that when
the fields have zero values, they should not be persisted in the object.
Before this commit, some of the metadata accessors for unstructured
objects did not respect these semantics i.e they would persist a field
even if it had a zero value.
This commit updates the accessors so that the field is removed from the
unstructured object map if it contains a zero value.
f69544e87d