code: public <T> ImmutableSet<T> objectsFromNamespaces(String baseNamespace,
        String activeNamespacesFeature,
        NamespaceToObjectMapper<? extends T> nameSpaceToObjectMapper) {
      final Parameters subNamespace = copyNamespace(baseNamespace);
      final ImmutableSet.Builder<T> ret = ImmutableSet.builder();
      for (final String activeNamespace : subNamespace.getStringList(activeNamespacesFeature)) {
        if (subNamespace.isNamespacePresent(activeNamespace)) {
          ret.add(nameSpaceToObjectMapper.fromNameSpace(subNamespace.copyNamespace(activeNamespace)));
        } else {
          throw new ParameterException("Expected namespace " + baseNamespace + DELIM + activeNamespace
              + "to exist because of value of " + activeNamespacesFeature + " but "
              + "it did not");
        }
      }
      return ret.build();
    }
docs: Gets objects defined by namespaces. It frequently happens that a program needs to have
  specified some set of objects to use, where each object is defined by some namespace. For
  example, in the name finder, we might need to use a number of different name set groups, where
  each group is defined by either a single name list or a map of name list names to name lists.
  Using this we would have a parameter file like this:
  <pre>
  # note foo is not used
  com.bbn.serif.names.lists.activeListGroups: standard,geonames,single
  com.bbn.serif.names.lists.standard.mapFile: /nfs/.....
  com.bbn.serif.names.lists.geonames.mapFile: /nfs/....
  com.bbn.serif.names.lists.foo.listPath: /nfs/....
  com.bbn.serif.names.lists.foo.listName: single
  com.bbn.serif.names.lists.foo.listPath: /nfs/...
  com.bbn.serif.names.lists.foo.listName: foo
  </pre>
  
  The user could load these by {@code objectsFromNameSpace("com.bbn.serif.names.lists",
  "activeListGroups", aNameSpaceToObjectMapperImplementation)}.
  
  If {@code activeNameSpacesFeature} is absent this will thrown a {@link ParameterException}.