How to bind nested List object to JSP form?

Hello fellow programmers,

I am writing a Spring MVC application for students to do an online assessment with multiple choice questions. An admin should be able to create assessments, so I created this object structure:

@Entity
@Table(name = "assessment")
public class Assessment {
    private List<Question> questions;
    // getter and setter
}


@Entity
@Table(name = "question")
public class Question {
    private String questionText;
    private List<Answer> answers;
    // getters and setters
}


@Entity
@Table(name = "answer")
public class Answer {
    private String answerText;
    private boolean isCorrect;
    // getters and setters
}

Now, I am using a JSP form on the admin page:

Controller

@RequestMapping(value = "/add/assessment", method = RequestMethod.GET)
public String addAssessments(Model model) {
    model.addAttribute("assessmentModel", new Assessment());

    return "admin-assessments-create";
}

JSP form

<form:form method="POST" modelAttribute="assessmentModel">
    <form:input path="questions[0].questionText" type="text"/> <!-- this is working-->

    <form:radiobutton path="questions[0].answers[0].isCorrect"/> <!-- not working-->
    <form:input path="questions[0].answers[0].answerText"/>

    <button class="btn" type="submit">Submit</button>
</form:form>

When I go to this page I receive the following error:

org.springframework.beans.NotReadablePropertyException:
    Invalid property 'questions[0].answers[0].isCorrect' of bean class [com.johndoe.model.Question]:
    Bean property 'questions[0].answers[0].isCorrect' is not readable or has an invalid getter method:
    Does the return type of the getter match the parameter type of the setter?

I checked all the getters and setters but those are perfectly fine.

Question:

how do I avoid the NotReadablePropertyException and thus bind the nested Answer List to my form?