fix: remove function call from kwarg (#19072)

this commit fixes mail not being sent for leave applications

Signed-off-by: Chinmay D. Pai <chinmaydpai@gmail.com>
diff --git a/erpnext/hr/doctype/leave_application/leave_application.py b/erpnext/hr/doctype/leave_application/leave_application.py
index d4da9c1..737f602 100755
--- a/erpnext/hr/doctype/leave_application/leave_application.py
+++ b/erpnext/hr/doctype/leave_application/leave_application.py
@@ -439,7 +439,7 @@
 	return ret
 
 @frappe.whitelist()
-def get_leave_balance_on(employee, leave_type, date, to_date=nowdate(), consider_all_leaves_in_the_allocation_period=False):
+def get_leave_balance_on(employee, leave_type, date, to_date=None, consider_all_leaves_in_the_allocation_period=False):
 	'''
 		Returns leave balance till date
 		:param employee: employee name
@@ -449,6 +449,9 @@
 		:param consider_all_leaves_in_the_allocation_period: consider all leaves taken till the allocation end date
 	'''
 
+	if not to_date:
+		to_date = nowdate()
+
 	allocation_records = get_leave_allocation_records(employee, date, leave_type)
 	allocation = allocation_records.get(leave_type, frappe._dict())
 
@@ -753,4 +756,4 @@
 		leave_approver = frappe.db.get_value('Department Approver', {'parent': department,
 			'parentfield': 'leave_approvers', 'idx': 1}, 'approver')
 
-	return leave_approver
\ No newline at end of file
+	return leave_approver