Field description for value_map does not match actual behavior

Problem/Motivation

The value_map field, labeled Value conversions, states that "If this is left empty, the values from the IdP will be interpreted as machine names for Drupal roles."

However, if it is left empty, role mapping is skipped, with the logged message: "value_map is not configured; skipping role mapping."

Steps to reproduce

1. Configure idp to have SAML attribute with Drupal roles
2. Enable role mapping and set SAML attribute but leave Value conversions empty.
3. Login with SAML
4. See that mapping does not work and the above error message logged

Proposed resolution

Either implement the described feature OR remove it from description