field `accessory` of type `Transaction` is not invalidated (moved or destroyed). not invalidated - flow cadence

Question

I'm developing a game and I have an avatar resource with the following definition that stores accessory NFTs and includes an equip function that returns any accessory that was existing in the slot

pub resource Avatar {
        pub let id: UInt64
        pub let accessories: @{String: Accessory}

        init() {
            self.id = Avatar.totalMinted + 1
            self.accessories <- {}

            Avatar.totalMinted = Avatar.totalMinted + 1
        }

        destroy () {
            Avatar.totalAvatars = Avatar.totalAvatars - 1
            destroy self.accessories
        }

        pub fun equip(accessory: @Accessory): @Accessory? {
            // Shift accessory into accessories dictionary and return old accessory
            let oldAccessory <- self.accessories[accessory.getAccessoryData().slot] <- accessory
            return <- oldAccessory

        }
}

Now in my transaction I get the accessory from my collection and equip it, making sure i deposit the old accessory in the slot if that exists.

import Avatar from 0x03
import NonFungibleToken from 0x01
transaction(avatarId: UInt64, accessoryId: UInt64) {
    
    let collection: &Avatar.Collection
    let avatar: auth &Avatar.Avatar
    let accessory: @Avatar.Accessory

    prepare(signer: AuthAccount) {
        self.collection = signer.borrow<&Avatar.Collection>(from: Avatar.CollectionStoragePath) ?? panic("could not borrow collection")
        self.avatar = self.collection.borrowAuth(id: avatarId) as? auth &Avatar.Avatar ?? panic("problem")
        self.accessory <- self.collection.withdraw(withdrawID: accessoryId) as! @Avatar.Accessory
    }

    execute {
        if let oldAccessory <- self.avatar.equip(accessory: <- self.accessory) {
            self.collection.deposit(token: <- oldAccessory)
        }

    }
}

I get the error field accessory of type Transaction is not invalidated (moved or destroyed). not invalidated - flow cadence

I have a feeling the type checker may not understand that the resource should be moved/destroyed by the end of this but maybe it's confused since it hands over the custody to Avatar.

Am I missing something?

Answer 1

Have you tried not using if let here? I am not sure that the compiler is smart enough to understand that the return from equip is nil even though you use if let