Regex enable if value is not empty or null

[sachinda123456]

I have some regex pattern Called discount discount: { type: 'string', pattern: /(^\d+(.\d{2})?$){0,100}/ },
It enable max allow two decimal places and minimum number is 0 and max number is 100 . According to my requirement everything fine . But i need to check this regex pattern if discount field has a value . That mean i need to disable pattern check if key does not have value . how can i achieve this .Because current situation use not able to allow null in discount field .

[intech]

add option in discount: optional: true