@Override
        public String toString() {
            return MoreObjects.toStringHelper(this)
                              .add("parameters", params)
                              .toString();
        }
Returns the first value of the parameter with the specified {@code name}. If it does not exist,
{@code null} is returned.
saml/src/main/java/com/linecorp/armeria/server/saml/SamlService.java