SOLR Atomic Update - String multiValued Field

[Doss]

HI,

I have a multiValued field of type String.

<field name="namelist" type="string"  indexed="true" stored="true"
multiValued="true"/>

I want to keep this list unique, so I am using atomic updates with
"add-distinct"

{"docid":123456,"namelist":{"add-distinct":["Adam","Jane"]}}

but this is not maintaining the expected uniqueness, am I doing something
wrong? Guide me please.

Thanks,
Doss.