Axis2 / Java: java.lang.NullPointerException at org.apache.axis2.context.MessageContext.isFault(MessageContext.java:4304)

Hi All!

I have deployed archive of services which consume/produce XMLs and now 
I'm trying to add one more service who will consume/produce JSON.
It is simple service which operates with POJOs.

To enable JSON operations I added to axis2.xml:

         <messageFormatter contentType="application/json"
class="org.apache.axis2.json.gson.JsonFormatter" />

<messageBuilder contentType="application/json"
class="org.apache.axis2.json.gson.JsonBuilder" />

In services XML I have declared my service:

<service name="LoginWSManager">
     <Description>
         This is a sample service to test json implementation
     </Description>
     <messageReceivers>
         <messageReceiver mep="http://www.w3.org/ns/wsdl/in-out"
class="org.apache.axis2.json.gson.rpc.JsonRpcMessageReceiver"  />
         <messageReceiver mep="http://www.w3.org/ns/wsdl/in-only"
class="org.apache.axis2.json.gson.rpc.JsonInOnlyRPCMessageReceiver"/>
     </messageReceivers>
     <parameter name="ServiceClass" 
locked="false">security.LoginWSManager</parameter>
</service>

Service code:

public LoginResponseWSBean login(String email, String password)throws Exception {
     Application.logger().info("Logging in user email: " + email);

     final LoginResponseWSBean loginResponseWSBean =new LoginResponseWSBean();
     try {
         loginBusinessLogic.login(email, password);
     }catch (Exception e) {
         loginResponseWSBean.setLoggedIn(false);
         loginResponseWSBean.setMessage(e.getMessage());
         loginResponseWSBean.setStackTrace(ExceptionUtils.getStackTrace(e));
         Application.logger().warning(String.format("Returning: %s", loginResponseWSBean));
         return loginResponseWSBean;
     }
     loginResponseWSBean.setLoggedIn(true);
     loginResponseWSBean.setMessage(email +" logged in successfully!");

     return loginResponseWSBean;
}

public class LoginResponseWSBeanimplements Serializable {

     private boolean loggedIn =false;
     private Stringmessage ="";
     private StringstackTrace ="";

     public LoginResponseWSBean(boolean loggedIn, String message, String stackTrace) {
         this.loggedIn = loggedIn;
         this.message = message;
         this.stackTrace = stackTrace;
     }

     public LoginResponseWSBean() {

     }
....
}


When I call it by this command:

curl -X POST -H "Content-Type: application/json" -d 
"{'login':[{'email':'[email protected]'}, {'password':'secret'}]}" 
http://localhost:8080/axis2/services/LoginWSManager/login

It responds with this message:
{"Fault":{"faultcode":"soapenv:Server","faultstring":"java.lang.NullPointerException","detail":""}}

In tomcat logs I can see this stacktrace:

30-Aug-2018 23:38:09.137 INFO [http-nio-8080-exec-9] 
org.apache.catalina.core.StandardWrapperValve.invoke [ERROR]
java.lang.NullPointerException
         at 
org.apache.axis2.context.MessageContext.isFault(MessageContext.java:4304)
         at 
org.apache.axis2.transport.http.CommonsHTTPTransportSender.sendUsingOutputStream(CommonsHTTPTransportSender.java:289)
         at 
org.apache.axis2.transport.http.CommonsHTTPTransportSender.invoke(CommonsHTTPTransportSender.java:244)
         at org.apache.axis2.engine.AxisEngine.send(AxisEngine.java:431)
         at 
org.apache.axis2.receivers.AbstractInOutMessageReceiver.invokeBusinessLogic(AbstractInOutMessageReceiver.java:43)
         at 
org.apache.axis2.receivers.AbstractMessageReceiver.receive(AbstractMessageReceiver.java:106)
         at org.apache.axis2.engine.AxisEngine.receive(AxisEngine.java:169)
         at 
org.apache.axis2.transport.http.HTTPTransportUtils.processHTTPPostRequest(HTTPTransportUtils.java:178)
         at 
org.apache.axis2.transport.http.AxisServlet.doPost(AxisServlet.java:163)
         at javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
         at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
         at 
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
         at 
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
         at 
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
         at 
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
         at 
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
         at 
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197)
         at 
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
         at 
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
         at 
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
         at 
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
         at 
org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
         at 
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
         at 
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:528)
         at 
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1100)
         at 
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:687)
         at 
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1520)
         at 
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1476)
         at 
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
         at 
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
         at 
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
         at java.lang.Thread.run(Thread.java:745)

Please help me find out why it is not processing LoginResponseWSBean 
response object as expected and generates NPE.
Thanx!

Alex