Batch Enroll of Student

**To Reproduce**
Steps to reproduce the behavior:
1. Create a new batch
2. Enroll a student
3. Get the following error:

Traceback (most recent call last): File "apps/frappe/frappe/utils/jinja.py", line 156, in render_template return compiled_template.render(context) ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^ File "env/lib/python3.14/site-packages/jinja2/environment.py", line 1295, in render self.environment.handle_exception() ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^ File "env/lib/python3.14/site-packages/jinja2/environment.py", line 942, in handle_exception raise rewrite_traceback_stack(source=source) File "", line 3, in top-level template code File "env/lib/python3.14/site-packages/jinja2/sandbox.py", line 401, in call return __context.call(__obj, *args, **kwargs) ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^ TypeError: 'NoneType' object is not callable

This also happens when you try to enroll a student via the Desk App.

To stop this from happening someone has to check the "Confirmation Email Sent" checkbox and then hit save in the Desk app. In the front end LMS app, you can't check this checkbox and it auto-fails.

**Expected behavior**
Enroll the selected student

**Screenshots**

**Desktop (please complete the following information):**
- OS: Windows 11
- Browser Vivaldi 8.0.4033.44 (Official Build) (64-bit)

**Additional context**
LMS Version:

frappe@21666dcaff96:~/frappe-bench$ bench version
frappe 16.21.0 ()
lms 2.55.0 ()
payments 0.0.1 ()
print_designer 1.6.7 ()

Start by reproducing batch enrollment from the Desk app and LMS app, then inspect the traceback's apps/frappe/frappe/utils/jinja.py:156 entry point and the enrollment flow that renders the template. Trace why the confirmation-email callback is None when the checkbox is unset. Done means enrolling a selected student succeeds from both interfaces without manually checking "Confirmation Email Sent."

Written by the indexing model from the issue text.