Erorr: cannot index into value which has type: `{Address: UInt8}?`

1 
pub struct AirDrop  {
    pub var allowActive: Bool
    pub let allowList:{Address: UInt8}
}

pub fun isAirDropWhiteList(itemId: String, user: Address): UInt8 {
    pre {
        self.tokenIdToAirDrop.containsKey(itemId): "Box cannot be overwritten"
    }
    **return  self.tokenIdToAirDrop[itemId]?.allowList[user]!**
}