TypeError occured on front-end when using the 'extra_classes=readonly' argument for the Select2Widget

Environment

Flask-Appbuilder version: 4.3.10

pip freeze output:

apispec==6.4.0 attrs==23.2.0 Babel==2.14.0 click==8.1.7 colorama==0.4.6 Deprecated==1.2.14 dnspython==2.4.2 email-validator==1.3.1 Flask==2.2.5 Flask-AppBuilder==4.3.10 Flask-Babel==2.0.0 Flask-JWT-Extended==4.6.0 Flask-Limiter==3.5.0 Flask-Login==0.6.3 Flask-SQLAlchemy==2.5.1 flask-wtf==1.2.1 greenlet==3.0.3 idna==3.6 importlib-metadata==7.0.1 importlib-resources==6.1.1 itsdangerous==2.1.2 Jinja2==3.1.3 jsonschema==4.20.0 jsonschema-specifications==2023.12.1 limits==3.7.0 markdown-it-py==3.0.0 MarkupSafe==2.1.3 marshmallow==3.20.2 marshmallow-sqlalchemy==0.26.1 mdurl==0.1.2 ordered-set==4.1.0 packaging==23.2 prison==0.2.1 pygments==2.17.2 PyJWT==2.8.0 python-dateutil==2.8.2 pytz==2023.3.post1 PyYAML==6.0.1 referencing==0.32.1 rich==13.7.0 rpds-py==0.17.1 six==1.16.0 SQLAlchemy==1.4.51 SQLAlchemy-Utils==0.41.1 typing-extensions==4.9.0 werkzeug==2.3.8 wrapt==1.16.0 wtforms==3.1.2 zipp==3.17.0

Describe the expected results

Tell us what should happen.

Department field on the edit view for employees is readonly.

Describe the actual results

Tell us what happens instead.

Department field on the edit view for employees can be changed.

Steps to reproduce

Correct the example:

provide get_pk_func method

   class EmployeeView(ModelView):
        datamodel = SQLAInterface(Employee)

        list_columns = ["full_name", "department.name", "employee_number"]
        edit_form_extra_fields = {
            "department": QuerySelectField(
                "Department",
                query_func=department_query,
                get_pk_func=lambda obj: obj.id,
                widget=Select2Widget(extra_classes="readonly"),
            )
        }

        related_views = [EmployeeHistoryView]
        show_template = "appbuilder/general/model/show_cascade.html"

Run the employees application from the examples in the flask-appbuilder repo. Create a function. Create a benefit. Create a department. Create a employee. Open the edit view for the employees in the web browser. Start the developer tools (F12).

dpgaspar / Flask-AppBuilder