SELECT max(item.id) FROM Table not working - jpa

Question

I'm trying to run this query SELECT max(item.id) FROM Table, but it returns javax.persistence.PersistenceException: java.lang.NullPointerException. The table is not empty. I tried it in PHPMyAdmin and it works.
This is my code:
public Long generateId(String beanName, String idName) {
String requete = "SELECT max(item." + idName + ") FROM " + beanName + " item";
List<Long> maxId = getEntityManager().createQuery(requete).getResultList();
if (maxId == null || maxId.isEmpty() || maxId.get(0) == null) {
return 1L;
}
return maxId.get(0) + 1;
}
The relevant stack:
Caused by: javax.persistence.PersistenceException: java.lang.NullPointerException
at org.eclipse.persistence.internal.jpa.QueryImpl.getResultList(QueryImpl.java:480)
at service.AbstractFacade.generateId(AbstractFacade.java:61)
at service.NotificationFacade.preparerNotification37(NotificationFacade.java:340)
at service.NotificationFacade.estimerMontantNotification(NotificationFacade.java:417)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.glassfish.ejb.security.application.EJBSecurityManager.runMethod(EJBSecurityManager.java:1081)
at org.glassfish.ejb.security.application.EJBSecurityManager.invoke(EJBSecurityManager.java:1153)
at com.sun.ejb.containers.BaseContainer.invokeBeanMethod(BaseContainer.java:4786)
at com.sun.ejb.EjbInvocation.invokeBeanMethod(EjbInvocation.java:656)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:608)
at org.jboss.weld.ejb.AbstractEJBRequestScopeActivationInterceptor.aroundInvoke(AbstractEJBRequestScopeActivationInterceptor.java:46)
at org.jboss.weld.ejb.SessionBeanInterceptor.aroundInvoke(SessionBeanInterceptor.java:52)
at sun.reflect.GeneratedMethodAccessor95.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:608)
at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.doCall(SystemInterceptorProxy.java:163)
at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.aroundInvoke(SystemInterceptorProxy.java:140)
at sun.reflect.GeneratedMethodAccessor94.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
at com.sun.ejb.containers.interceptors.InterceptorManager.intercept(InterceptorManager.java:369)
at com.sun.ejb.containers.BaseContainer.__intercept(BaseContainer.java:4758)
at com.sun.ejb.containers.BaseContainer.intercept(BaseContainer.java:4746)
at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:212)
... 54 more
Caused by: java.lang.NullPointerException
at org.eclipse.persistence.internal.sessions.CollectionChangeRecord.addAdditionChange(CollectionChangeRecord.java:106)
at org.eclipse.persistence.internal.queries.ContainerPolicy.compareCollectionsForChange(ContainerPolicy.java:560)
at org.eclipse.persistence.mappings.CollectionMapping.compareCollectionsForChange(CollectionMapping.java:574)
at org.eclipse.persistence.mappings.CollectionMapping.calculateDeferredChanges(CollectionMapping.java:541)
at org.eclipse.persistence.descriptors.changetracking.AttributeChangeTrackingPolicy.createObjectChangeSet(AttributeChangeTrackingPolicy.java:75)
at org.eclipse.persistence.descriptors.changetracking.DeferredChangeDetectionPolicy.calculateChanges(DeferredChangeDetectionPolicy.java:91)
at org.eclipse.persistence.descriptors.changetracking.AttributeChangeTrackingPolicy.calculateChangesForExistingObject(AttributeChangeTrackingPolicy.java:48)
at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.calculateChanges(UnitOfWorkImpl.java:664)
at org.eclipse.persistence.internal.sessions.RepeatableWriteUnitOfWork.writeChanges(RepeatableWriteUnitOfWork.java:438)
at org.eclipse.persistence.internal.jpa.EntityManagerImpl.flush(EntityManagerImpl.java:863)
at org.eclipse.persistence.internal.jpa.QueryImpl.performPreQueryFlush(QueryImpl.java:963)
at org.eclipse.persistence.internal.jpa.QueryImpl.executeReadQuery(QueryImpl.java:207)
at org.eclipse.persistence.internal.jpa.QueryImpl.getResultList(QueryImpl.java:469)
... 86 more