Navigating to "Edit Course" --> "Instances" throws error

[murhum1]

Navigating to "Edit Course" --> "Instances" throws an error in cases where SIS enrollment is enabled, but the course doesn't have an instance in SIS. This generates unnecessary error emails that do not require admin intervention.

The exception is thrown in

a-plus/edit_course/course_forms.py

Lines 334 to 358 in 8e2f835

	def set_sis_selector(self) -> None:
	sis: StudentInfoSystem = get_sis_configuration()
	if not sis:
	# Student Info System not configured
	return
	try:
	instances = sis.get_instances(self.instance.course.code)
	# If there are no SIS instances by this course code, don't show menu or checkbox
	if instances:
	options = [('none', '---------')] + instances
	self.fields['sis'] = forms.ChoiceField(
	choices=options,
	label=_('LABEL_SIS_INSTANCE'),
	help_text=_('LABEL_SIS_INSTANCE_HELPTEXT'),
	)
	self.fields['sis_enroll'] = forms.BooleanField(
	label=_('LABEL_SIS_ENROLL'),
	help_text=_('LABEL_SIS_ENROLL_HELPTEXT'),
	required=False,
	initial=False,
	)
	except Exception:
	logger.exception("Error getting instances from SIS.")

. There should probably be a way of handling specific HTTP error codes - e.g. 404 in this case - in sis.get_instances code.