IllegalArgumentException: id to load is required for loading В чем сдесь проблема?

Как только программа заходит в метод loginClient выкидывает IllegalArgumentException: id to load is required for loading. Cуть метода получить ввод юзера из html формы, найти юзера по юзернайм в базе и сверить введенные и данные в базе.

@PostMapping("/login")
    public String loginClient(@ModelAttribute("input") Input input) throws Exception {
        String page = "";
        userInput = input.getPostUsername();
        Client existingClient = service.getClient(userInput);
        if((input.getPostUsername().equals(existingClient.getUsername())&
                (input.getPostPassword().equals(existingClient.getPassword())))){
            page = "Auth";
            SpotifyAPI newApi = new SpotifyAPI();
            newApi.startServer(8081);
        }
        else{
            page = "index";
        }
        return page;

 <form method="post" th:action="@{/login}" th:object="${input}" class="login">
    <p>
        <label th:for="postUsername">Username: </label>
        <input type="text" th:name="postUsername" id="postUsername"/>
    </p>

    <p>
        <label th:for="postPassword">Password: </label>
        <input type="text" th:name="postPassword" id="postPassword"/>
    </p>

java.lang.IllegalArgumentException: id to load is required for loading
    org.hibernate.event.spi.LoadEvent.<init>(LoadEvent.java:93)
    org.hibernate.event.spi.LoadEvent.<init>(LoadEvent.java:63)
    org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.doLoad(SessionImpl.java:2920)
    org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.lambda$load$1(SessionImpl.java:2904)
    org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.perform(SessionImpl.java:2860)
    org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.load(SessionImpl.java:2904)
    org.hibernate.internal.SessionImpl.get(SessionImpl.java:1097)
    spotify.repository.ClientDAOImpl.getCustomer(ClientDAOImpl.java:58)
    spotify.service.ClientServiceImpl.getClient(ClientServiceImpl.java:41)
    java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.base/java.lang.reflect.Method.invoke(Method.java:567)
    org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:344)
    org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:198)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
    org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:294)
    org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:98)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212)
    com.sun.proxy.$Proxy46.getClient(Unknown Source)
    spotify.controller.AppControl.loginClient(AppControl.java:31)

ClientServiceImpl class:

@Override
    @Transactional
    public Client getClient(String username) {

        return clientDAO.getCustomer(username);
    }

DAOimpl

@Override
    public Client getCustomer(String username) {

        // get the current hibernate session
        Session currentSession = sessionFactory.getCurrentSession();

        // now retrieve/read from database using the primary key

        return currentSession.get(Client.class, username);
    }