@PostConstruct method throws NPE when called on a stateless session bean.
The method iteself accesses the enetity manager and tries create a query, the following exception is experienced:

java.lang.RuntimeException: java.lang.NullPointerException
at org.jboss.ejb3.interceptor.LifecycleInterceptorHandler.postConstruct(LifecycleInterceptorHandler.java:109)
at org.jboss.ejb3.EJBContainer.invokePostConstruct(EJBContainer.java:582)
at org.jboss.ejb3.AbstractPool.create(AbstractPool.java:108)
at org.jboss.ejb3.ThreadlocalPool.get(ThreadlocalPool.java:48)
at org.jboss.ejb3.stateless.StatelessInstanceInterceptor.invoke(StatelessInstanceInterceptor.java:54)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
at org.jboss.aspects.security.AuthenticationInterceptor.invoke(AuthenticationInterceptor.java:78)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
at org.jboss.ejb3.ENCPropagationInterceptor.invoke(ENCPropagationInterceptor.java:47)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
at org.jboss.ejb3.asynchronous.AsynchronousInterceptor.invoke(AsynchronousInterceptor.java:106)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
at org.jboss.ejb3.stateless.StatelessContainer.dynamicInvoke(StatelessContainer.java:227)
at org.jboss.aop.Dispatcher.invoke(Dispatcher.java:106)
at org.jboss.aspects.remoting.AOPRemotingInvocationHandler.invoke(AOPRemotingInvocationHandler.java:82)
at org.jboss.remoting.ServerInvoker.invoke(ServerInvoker.java:828)
at org.jboss.remoting.ServerInvoker.invoke(ServerInvoker.java:681)
at org.jboss.remoting.transport.socket.ServerThread.processInvocation(ServerThread.java:358)
at org.jboss.remoting.transport.socket.ServerThread.dorun(ServerThread.java:398)
at org.jboss.remoting.transport.socket.ServerThread.run(ServerThread.java:239)
Caused by: java.lang.NullPointerException
at org.jboss.ejb3.entity.ManagedEntityManagerFactory.getNonTxEntityManager(ManagedEntityManagerFactory.java:58)
at org.jboss.ejb3.entity.ManagedEntityManagerFactory.getTransactionScopedEntityManager(ManagedEntityManagerFactory.java:163)
at org.jboss.ejb3.entity.TransactionScopedEntityManager.createQuery(TransactionScopedEntityManager.java:125)
at com.teleglobal.modules.snapaccount.services.SnapAccountSendProcessServiceBean.initialiseSpendCardQuery(SnapAccountSendProcessServiceBean.java:83)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.jboss.ejb3.interceptor.LifecycleInvocationContextImpl.proceed(LifecycleInvocationContextImpl.java:159)
at org.jboss.ejb3.interceptor.LifecycleInterceptorHandler.postConstruct(LifecycleInterceptorHandler.java:105)
at org.jboss.ejb3.EJBContainer.invokePostConstruct(EJBContainer.java:582)
at org.jboss.ejb3.AbstractPool.create(AbstractPool.java:108)
at org.jboss.ejb3.ThreadlocalPool.get(ThreadlocalPool.java:48)
at org.jboss.ejb3.stateless.StatelessInstanceInterceptor.invoke(StatelessInstanceInterceptor.java:54)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
at org.jboss.aspects.security.AuthenticationInterceptor.invoke(AuthenticationInterceptor.java:78)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
at org.jboss.ejb3.ENCPropagationInterceptor.invoke(ENCPropagationInterceptor.java:47)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
at org.jboss.ejb3.asynchronous.AsynchronousInterceptor.invoke(AsynchronousInterceptor.java:106)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
at org.jboss.ejb3.stateless.StatelessContainer.dynamicInvoke(StatelessContainer.java:227)
at org.jboss.aop.Dispatcher.invoke(Dispatcher.java:106)
at org.jboss.aspects.remoting.AOPRemotingInvocationHandler.invoke(AOPRemotingInvocationHandler.java:82)
at org.jboss.remoting.ServerInvoker.invoke(ServerInvoker.java:828)
at org.jboss.remoting.ServerInvoker.invoke(ServerInvoker.java:681)
at org.jboss.remoting.transport.socket.ServerThread.processInvocation(ServerThread.java:358)
at org.jboss.remoting.transport.socket.ServerThread.dorun(ServerThread.java:398)
at org.jboss.remoting.transport.socket.ServerThread.run(ServerThread.java:239)
at org.jboss.remoting.RemoteClientInvoker.invoke(RemoteClientInvoker.java:190)
at org.jboss.remoting.Client.invoke(Client.java:525)
at org.jboss.remoting.Client.invoke(Client.java:488)
at org.jboss.aspects.remoting.InvokeRemoteInterceptor.invoke(InvokeRemoteInterceptor.java:55)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
at org.jboss.aspects.tx.ClientTxPropagationInterceptor.invoke(ClientTxPropagationInterceptor.java:61)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
at org.jboss.aspects.security.SecurityClientInterceptor.invoke(SecurityClientInterceptor.java:55)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
at org.jboss.ejb3.remoting.IsLocalInterceptor.invoke(IsLocalInterceptor.java:78)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
at org.jboss.ejb3.stateless.StatelessRemoteProxy.invoke(StatelessRemoteProxy.java:102)
at $Proxy3.getBatchNumbers(Unknown Source)
at com.teleglobal.modules.snapaccount.services.SnapAccountSendProcessServiceTest.testGetBatchNumbers(SnapAccountSendProcessServiceTest.java:57)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at junit.framework.TestCase.runTest(TestCase.java:154)
at junit.framework.TestCase.runBare(TestCase.java:127)
at junit.framework.TestResult$1.protect(TestResult.java:106)
at junit.framework.TestResult.runProtected(TestResult.java:124)
at junit.framework.TestResult.run(TestResult.java:109)
at junit.framework.TestCase.run(TestCase.java:118)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:478)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:344)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)

Here is a the post construct method:

@PostConstruct
void initialiseSpendCardQuery()
{
StringBuilder sendCardQueryString = new StringBuilder();
sendCardQueryString.append("SELECT c FROM Card AS c WHERE c.status = 'U' AND c.batchNumber IN (");

long[] batchNumbers = getBatchNumbers();
for (int i = 0; i < batchNumbers.length; i++)

{ sendCardQueryString.append("?").append(i); if (i+1 < batchNumbers.length) sendCardQueryString.append(","); }

sendCardQueryString.append(") AND c NOT IN (SELECT lc.sendCard FROM SendCardLock AS lc)");
sendCardQuery = entityManager.createQuery(sendCardQueryString.toString());

for (int i = 0; i < batchNumbers.length; i++)
sendCardQuery.setParameter(i, batchNumbers[i]);
}

It happens when the entityManager is used.