org.apache.cxf.interceptor.Fault: null while invoking public java.lang.String JaxRS server

@GET
@Path("/freePlaces")
@Produces("application/json")
public String places(@QueryParam("projectionId") String projectionId) {
    return projectionDAO.findById(Long.parseLong(projectionId)).getPlaces().toString();
}

I have this simple method and when I write in the url:

http://localhost:8080/cinema/rest/projection/freePlaces?projectionId=351

I get this exception :

java.lang.RuntimeException: org.apache.cxf.interceptor.Fault: null while invoking public java.lang.String cinema.services.ProjectionManager.places(java.lang.String) with params [351]. org.apache.cxf.interceptor.Fault: null while invoking public java.lang.String cinema.services.ProjectionManager.places(java.lang.String) with params [351].

I need some help how to resolve this.