FLASK – Updating Form without updating certain fields causes 400 Bad Request Error

Solution
werkzeug.exceptions.BadRequestKeyError: 400 Bad Request: 
The browser (or proxy) sent a request that this server could not understand. 
KeyError: 'eligible_applicant_category'
if 'name_of_filed' in request.form:
    my_field = request.form['name_of_filed']
my_field = request.form.get('name_of_filed', 'default_value')