private LinkedHashMap<String, String> getMessages() {
        if (internalMessages == null) {
            internalMessages = initializeSession();
        }
        return internalMessages;
    }
Provides message store hashtable. Table is lazily initialized when user tries to store or retrieve
the first message.

@return message store
pac4j-saml/src/main/java/org/pac4j/saml/store/HttpSessionStore.java