@Override
    protected void doInitialize() throws ComponentInitializationException {
        LOGGER.debug("Initialized {}", this.getClass().getSimpleName());
        if (getMessageContext() == null) {
            throw new ComponentInitializationException("Message context cannot be null");
        }
        if (getVelocityEngine() == null) {
            throw new ComponentInitializationException("VelocityEngine must be supplied");
        }
        if (getVelocityTemplateId() == null) {
            throw new ComponentInitializationException("Velocity template id must be supplied");
        }
    }
{@inheritDoc}

Check component attributes. Copy/Paste parents initialization (no super.doInitialize) except for
AbstractHttpServletResponseMessageEncoder since HttpServletResponse is always null.
pac4j-saml/src/main/java/org/pac4j/saml/transport/Pac4jHTTPPostSimpleSignEncoder.java