Detecting whether or not an object supports retention via REST API

Hello,

I would like to know if there is a reliable way to use the REST API to determine if a specific object is currently associated with a policy for which retention is supported. I have discovered by experimentation on my test system that if the current value of the user.maui.retentionEnd metadata attribute has a value of "NONE" (which I retrieved by issuing an HTTP HEAD request against the desired object), that a subsequent attempt to set that attribute to a valid ISO8601 GMT date value will fail; however if the current value is an ISO8601 GMT date, then I can update it to a different date value. Can I infer from this that a current value of "NONE" always means that the object is not associated with a Policy for which retention is supported? If not, is there alternative way to determine this?

Thanks,

-Eric