Converting String to Nominal attributes

I tried to put the Domain Calculator node before and also after the Rename node, but if I convert from StringValue to NominalValue I get the same resulting attributes Column Type:

Non-Native [interface org.knime.core.data.NominalValue, interface org.knime.core.data.StringValue, interface org.knime.core.data.DataValue]

How can I do to properly convert strings to nominals ?

Thank you again
Cheers
Carmelo