flexjson - error deserializando

I'm using the flexjson library to serialize / deserialize JSON files with Netbeans 8.2. If I try to deserialize the previously created JSON from the instance of class Xxx, an error occurs, indicating that it can not deserialize class Xxx.

  

java.lang.ClassCastException: java.util.HashMap can not be cast   flexjson_test.Main $ Xxx

Note: the JSONs are created correctly, I printed them on the screen.

I did several tests and it's always the same.

Test code:

package flexjson_test;

import flexjson.JSONDeserializer;
import flexjson.JSONSerializer;
import java.util.ArrayList;


public class Main {

    private JSONSerializer serializer;
    private JSONDeserializer<Project> projectDeserializer;
    private JSONDeserializer<Task> taskDeserializer;
    private String jsonProject, jsonTask;


    /**
     * Main method
     *
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        new Main();
    }

    /**
     * Constructor
     *
     */
    public Main() {
        serializer          = new JSONSerializer().exclude("*.class");
        projectDeserializer = new JSONDeserializer<>();
        taskDeserializer    = new JSONDeserializer<>();

        this.testSerialize();
        this.testDeserialize();
    }


    /**
     * Tests
     *
     */

    private void testDeserialize() {
        System.out.println("Deserialization tests...");
        Project project = this.deserialiceProject(this.jsonProject);
        Task task = this.deserialiceTask(this.jsonTask);

        System.out.println("-------------------------------------\n\n");
    }

    private void testSerialize() {
        System.out.println("Serialization tests...");
        Project project = getProject();
        Task task       = getTask();

        this.jsonTask = serializer.serialize( task );
        System.out.println("Task: \n" + jsonTask);

        this.jsonProject = serializer.serialize( project );
        System.out.println("Project: \n" + jsonProject);

        project.addTask(task);
        this.jsonProject = serializer.include( "tasks" ).serialize( project );
        System.out.println("Project: \n" + jsonProject);

        System.out.println("-------------------------------------\n\n");
    }

    /**
     * Deserialices
     *
     */

    private Project deserialiceProject(String json) {

        if ( json == null || json.equals("")) {
            System.err.println("ERR args-> deserializing Project");
            return null;
        }

        Project p = null;
        try {
            p = projectDeserializer.deserialize(json);
        } catch(Exception e) {
            System.err.println(
                "ERR -> deserializing Project -> " + e.toString( ));
        }

        return p;
    }

    private Task deserialiceTask(String json) {

        if ( json == null || json.equals("")) {
            System.err.println("ERR args-> deserializing Task");
            return null;
        }

        Task t = null;
        try {
            t = taskDeserializer.deserialize(json);
        } catch(Exception e) {
            System.err.println(
                "ERR -> deseriazing Task -> " + e.toString( ));
        }

        return t;
    }


    /**
     * Create entities
     *
     */

    private Task getTask() {
        Task t = new Task( 1, "task one" );
        System.out.println(t.toString( ));
        return t;
    }

    private Project getProject() {
        Project p = new Project( 1, "test" );
        System.out.println(p.toString( ));
        return p;
    }


    /**
     * Internal classes
     *
     */

    private class Project {
        private int id;
        private String name;
        private ArrayList<Task> tasks;

        public Project(int id, String name) {
            this.id   = id;
            this.name = name;

            this.tasks = new ArrayList<>();
        }
        public Project(int id, String name, ArrayList<Task> tasks) {
            this.id    = id;
            this.name  = name;
            this.tasks = tasks;
        }


        public void addTask(Task t) {
            if (t == null) {
                System.err.println("Error storing task: 'null' given");
                return;
            }

            this.tasks.add( t );
        }

        public void clearTasks() {
            this.tasks.clear();
        }

        // Getters and setters

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public ArrayList<Task> getTasks() {
            return tasks;
        }

        public void setTasks(ArrayList<Task> tasks) {
            this.tasks = tasks;
        }

    } // class

    private class Task {
        private int id;
        private String name;

        public Task(int id, String name) {
            this.id   = id;
            this.name = name;
        }

        // Getters and setters

        public int getId() {
            return id;
        }

        public String getName() {
            return name;
        }

        public void setId(int id) {
            this.id = id;
        }

        public void setName(String name) {
            this.name = name;
        }

    } // class

} // class