Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_20 ( extra_points INTEGER, points VARCHAR, field_goals VARCHAR )

### Question ###
What is the highest amount of extra points someone got when they scored 28 points but had 0 field goals?

### Accurate SQL ###

SELECT MAX(extra_points) FROM table_name_20 WHERE points = 28 AND field_goals < 0