boolean return value of automation operations are not well serialized in json encoding

When a client is invoking an automation operation returning a boolean value,
it cannot get back the result because an error during the json serialization.

The following error is printed in the error log

SEVERE: A message body writer for Java type, class java.lang.Boolean, and MIME media type, application/octet-stream, was not found

followed by the stack trace

15:44:35,931 ERROR [WebEngineExceptionMapper] Exception in JAX-RS processing
javax.ws.rs.WebApplicationException
at com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:268)
at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1029)
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:941)
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:932)
at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:384)
at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:451)
at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:632)
at org.nuxeo.ecm.webengine.jaxrs.servlet.JerseyServlet.superService(JerseyServlet.java:145)
at org.nuxeo.ecm.webengine.jaxrs.servlet.JerseyServlet.service(JerseyServlet.java:92)