Description
The implementation provided by ActiveMQ of javax.jms.Message.getObjectProperty(String) does not return a value when the property is JMSXUserID.
This causes a null pointer exception in org.apache.activemq.web.MessageServlet.setResponseHeaders as message.getObjectProperty(name).toString() is used within the loop.
Using javax.jms.Message.getStringProperty(String) solves the problem.
To reproduce, try to consume a message via the REST interface when the broker is configured with populateJMSXUserID="true" and useAuthenticatedPrincipalForJMSXUserID="true".