code: protected Map<String, List<Object>> toSeedMap(final String uid) {
          final List<Object> values = Collections.singletonList((Object) uid);
          final String usernameAttribute = this.usernameAttributeProvider.getUsernameAttribute();
          final Map<String, List<Object>> seed = Collections.singletonMap(usernameAttribute, values);
          if (this.logger.isDebugEnabled()) {
              this.logger.debug("Created seed map='" + seed + "' for uid='" + uid + "'");
          }
          return seed;
      }
docs: Converts the uid to a multi-valued seed Map using the value from {@link #getUsernameAttributeProvider()}
  as the key.
  
  @param uid userId
  @return multi-valued seed Map containing the uid