I think I'm a little mixed up with how the irregular adjectives work.
Latin: Nulli malo puero praedam dat magister.
nullus, -a, um (§108) is an irregular adjective that has the form nulli in the dataive singular. ("to none, to no")
puero is the dative singular or ablative singular (§91) of puer; the adjective malo agrees in case, gender, and number with puero (§65) "to the (from the) bad boy"
praedam is the ...