Minecraft Client Check if inventory is full?

So I program with clients and have no built in player p, so the question with which method I can check whether the inventory is full.

You go through all the slots from 0 to 35 and see if the slot is occupied. If all are occupied, then your inventory is full.

boolean isInventoryFull () {
for (int i = 0; i 6; i ++) {
if (mc.thePlayer.inventory?) {// Check if the respective slot is free - I just don't know how it works.
return false;
}
}
return true;
}