How can I deserialize part of a JSON string into an object, using FlexJSON?

Question

I'm trying to serialze part of a JSON string into an object. The JSON string looks as follows:

{"error":null,"excludeFields":null,"message":null,"success":{"user":{"name":null,"organizationId":100,"username":"nl4321"}}}

I only need the user-part of the JSON string, which corresponds to an object of the following class:

public class UserForm implements Serializable {

    private static final long serialVersionUID = -5033294929007794646L;
    private String username;
    private String name;
    @Getter @Setter
    private int organizationId;

    public UserForm() {
    }

    public UserForm(User user) {
        if (user != null) {
            this.username = user.getUsername();
            this.name = user.getName();
            this.organizationId = user.getDefaultOrganisationId();
        }
    }

    public String getName() {
        return name;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }
}

The way I'm currently trying to deserialize it, is as follows:

private UserForm deserializeToJsonResponse(String bodyContent) throws IOException {
        JSONDeserializer<UserForm> jsonDeserializer = new JSONDeserializer<UserForm>();
        return jsonDeserializer.use("values.success.user", UserForm.class).deserialize(bodyContent, UserForm.class);
}

The use method is provided with both a path and a class, but no matter what path I try, the contents of the UserForm are null after deserialization. I've tried: "user", "success.user", "values.success.user".

Does anyone have an idea what I'm doing wrong and how I can fix it? I realize there are other solutions out there, like Jackson, but this is part of a large codebase that already uses FlexJSON a lot. Background: I'm trying to write unit tests for an API that's part of the project.