code: public Parameters copyNamespaceIfPresent(final String requestedNamespace) {
      // checkArgument ensures namespaces are specified consistently
      checkArgument(!requestedNamespace.isEmpty());
      checkArgument(!requestedNamespace.endsWith(DELIM));
      if (isNamespacePresent(requestedNamespace)) {
        return copyNamespace(requestedNamespace);
      } else {
        return copy();
      }
    }
docs: If the specified namespace is present, return a copy of that namespace as a parameter set.
  Otherwise, return a copy of this parameter set. The name space name should *not* have a
  trailing ".".