java.lang.NullPointerException while extracting relevant fluent

[eyess-glitch]

I have the following domain and problem files

(define 
  (domain emergency-logistics)
  (:requirements :strips :typing :negative-preconditions :conditional-effects :disjunctive-preconditions)

  (:types 
    person box content location carrier agent value - object
  )

  (:constants
    zero one two three four - value
  )

  (:predicates
    (person-at-loc ?p - person ?l - location)
    (box-at-loc ?b - box ?l - location)
    (content-at-loc ?c - content ?l - location)
    (carrier-at-loc ?c - carrier ?l - location)
    (agent-at-loc ?a - agent ?l - location)   
    (is-box-empty ?b - box)
    (has-box-content ?c - content ?b - box)
    (has-person-content ?p - person ?c - content)
    (box-on-carrier ?b - box ?ca - carrier)
    (is-carrier-full ?c - carrier)
    (carrier-capacity ?c - carrier ?v - value)
    (total-boxes ?c - carrier ?v - value)
  )

  (:action FILL-BOX
    :parameters (?b - box ?c - content ?a - agent ?l - location)
    :precondition (and
      (box-at-loc ?b ?l)
      (agent-at-loc ?a ?l)
      (content-at-loc ?c ?l)
      (is-box-empty ?b)
    )
    :effect (and
      (not (is-box-empty ?b))
      (has-box-content ?c ?b)
    )
  )

  (:action EMPTY-BOX
    :parameters (?b - box ?c - content ?p - person ?l - location ?a - agent)
    :precondition (and
      (not (is-box-empty ?b))
      (not (has-person-content ?p ?c))
      (box-at-loc ?b ?l)
      (agent-at-loc ?a ?l)
      (has-box-content ?c ?b)
      (person-at-loc ?p ?l)
    )
    :effect (and
      (not (has-box-content ?c ?b))
      (has-person-content ?p ?c)
      (is-box-empty ?b)
      (content-at-loc ?c ?l)
    )
  )

  (:action PICK-AND-LOAD-BOX-ON-CARRIER
    :parameters (?b - box ?l - location ?a - agent ?c - carrier)
    :precondition (and
      (box-at-loc ?b ?l)
      (agent-at-loc ?a ?l)
      (carrier-at-loc ?c ?l)
      (not (box-on-carrier ?b ?c))
      (not (is-carrier-full ?c))
    )
    :effect (and
      (box-on-carrier ?b ?c)
      (not (box-at-loc ?b ?l))
      (when (total-boxes ?c zero) (and (not (total-boxes ?c zero)) (total-boxes ?c one)))
      (when (and (total-boxes ?c one) (carrier-capacity ?c two)) (and (not (total-boxes ?c one)) (total-boxes ?c two) (is-carrier-full ?c))) 
      (when (total-boxes ?c one) (and (not (total-boxes ?c one)) (total-boxes ?c two)))
      (when (and (total-boxes ?c two) (not (is-carrier-full ?c))) (and (not (total-boxes ?c two)) (total-boxes ?c three)))
      (when (and (total-boxes ?c three) (carrier-capacity ?c four)) (and (not (total-boxes ?c three)) (total-boxes ?c four) (is-carrier-full ?c))
      )
    )
  )

  (:action UNLOAD-CARRIER
    :parameters (?b - box ?c - carrier ?l - location ?a - agent)
    :precondition (and
      (agent-at-loc ?a ?l)
      (carrier-at-loc ?c ?l)
      (box-on-carrier ?b ?c)
    )
    :effect (and
      (when (total-boxes ?c one) (and (not (total-boxes ?c one)) (total-boxes ?c zero)))
      (when (total-boxes ?c two) (and (not (total-boxes ?c two)) (total-boxes ?c one)))
      (when (total-boxes ?c three) (and (not (total-boxes ?c three)) (total-boxes ?c two)))
      (when (total-boxes ?c four) (and (not (total-boxes ?c four)) (total-boxes ?c three)))
      ; modifico qua la capacità
      (when (and (carrier-capacity ?c four) (total-boxes ?c three)) (not (is-carrier-full ?c)))
      (when (and (carrier-capacity ?c two) (total-boxes ?c one)) (not (is-carrier-full ?c)))
      (not (box-on-carrier ?b ?c))
      (box-at-loc ?b ?l)
    )
  )

  (:action MOVE-CARRIER
    :parameters (?c - carrier ?l - location)
    :precondition (and
      (not (carrier-at-loc ?c ?l))
    )
    :effect (and
      (carrier-at-loc ?c ?l)
    )
  )

  (:action MOVE-AGENT
    :parameters (?a - agent ?c - carrier ?l - location)
    :precondition (and
      (not (agent-at-loc ?a ?l))
      (not (carrier-at-loc ?c ?l))
      ;(or (is-carrier-full ?c))
    )
    :effect (and
      (when (is-carrier-full ?c) (carrier-at-loc ?c ?l))
      (agent-at-loc ?a ?l)
    )
  )
)

(define 
  (problem emergency-logistics-instance)
  (:domain emergency-logistics)
  (:objects
    box1 box2 box3 box4 box5 - box
    food1 food2 medicine1 medicine2 - content
    depot location1 location2 - location
    carrier1 - carrier
    agent1 - agent
    person1 person2 person3 - person
  )

  (:init
    ; Box locations
    ; un box è ridondante
    (box-at-loc box1 depot)
    (box-at-loc box2 depot)
    (box-at-loc box3 depot)
    (box-at-loc box4 depot)
    (box-at-loc box5 depot)

    ; Content locations
    (content-at-loc food1 depot)
    (content-at-loc food2 depot)
    (content-at-loc medicine1 depot)
    (content-at-loc medicine2 depot)

    (person-at-loc person1 location1)
    (person-at-loc person2 location1)
    (person-at-loc person3 location2)

    (not (has-person-content person1 food1))
    (not (has-person-content person1 medicine1))
    (not (has-person-content person2 medicine2))
    (not (has-person-content person3 food2))

    ; Carrier location
    (carrier-at-loc carrier1 depot)

    ; Agent location
    (agent-at-loc agent1 depot)

    ; Empty box initial conditions
    (is-box-empty box1)
    (is-box-empty box2)
    (is-box-empty box3)
    (is-box-empty box4)
    (is-box-empty box5)

    (carrier-capacity carrier1 four)

    ; Initial carrier state
    (not (is-carrier-full carrier1))

    (total-boxes carrier1 zero)
    (not (total-boxes carrier1 one))
    (not (total-boxes carrier1 two))
    (not (total-boxes carrier1 three))
    (not (total-boxes carrier1 four))
  )

  (:goal
    (and
      (has-person-content person1 food1)
      (has-person-content person1 medicine1)
      (has-person-content person2 medicine2)
      (has-person-content person3 food2)
    )
  )
)

Both files are written in PDDL 1.2 (I cannot use the newer version of the language for several purpose). Based on the guide available on the site for pddl4j, I first tried instantiating the planning problem with the code

package fr.uga.pddl4j.examples;

import fr.uga.pddl4j.parser.DefaultParsedProblem;
import fr.uga.pddl4j.parser.ErrorManager;
import fr.uga.pddl4j.parser.Message;
import fr.uga.pddl4j.parser.Parser;
import fr.uga.pddl4j.problem.DefaultProblem;
import fr.uga.pddl4j.problem.Problem;
import fr.uga.pddl4j.problem.operator.Action;

import java.io.FileNotFoundException;

/**
 * The class is an example class. It shows how to use the library to create to ground planning problem.
 *
 * @author D. Pellier
 * @version 4.0 - 06.12.2021
 */
public class ProblemInstantiationExample {

    /**
     * The main method the class. The first argument must be the path to the PDDL domain description and the second
     * argument the path to the PDDL problem description.
     *
     * @param args the command line arguments.
     */
    public static void main(final String[] args) {

        // Checks the number of arguments from the command line
        if (args.length != 2) {
            System.out.println("Invalid command line");
            return;
        }

        try {
            // Creates an instance of the PDDL parser
            final Parser parser = new Parser();
            // Parses the domain and the problem files.
            final DefaultParsedProblem parsedProblem = parser.parse(args[0], args[1]);
            // Gets the error manager of the parser
            final ErrorManager errorManager = parser.getErrorManager();
            // Checks if the error manager contains errors
            if (!errorManager.isEmpty()) {
                // Prints the errors
                for (Message m : errorManager.getMessages()) {
                    System.out.println(m.toString());
                }
            } else {
                // Prints that the domain and the problem were successfully parsed
                System.out.print("\nparsing domain file \"" + args[0] + "\" done successfully");
                System.out.print("\nparsing problem file \"" + args[1] + "\" done successfully\n\n");
                // Create a problem
                final Problem problem = new DefaultProblem(parsedProblem);
                // Instantiate the planning problem
                problem.instantiate();
                // Print the list of actions of the instantiated problem
                for (Action a : problem.getActions()) {
                    //System.out.println(problem.toString(a));
                }
            }
            // This exception could happen if the domain or the problem does not exist
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}

though it gives the following error

Exception in thread "main" java.lang.NullPointerException at fr.uga.pddl4j.problem.FinalizedProblem.extractRelevantFluents(FinalizedProblem.java:373) at fr.uga.pddl4j.problem.DefaultProblem.finalization(DefaultProblem.java:299) at fr.uga.pddl4j.problem.AbstractProblem.instantiate(AbstractProblem.java:444) at fr.uga.pddl4j.examples.ProblemInstantiationExample.main(ProblemInstantiationExample.java:56)

I'm pretty sure the problem is related to the domain file or problem file since I tried executing the same code on different problems and domains and it worked