NFTProviderAggregator: Make borrowNFT return Optional(NFT) (#96)

* make borrowNFT return Optional

* add test script

Author: sid42

nft-provider-aggregator/contracts/NFTProviderAggregator.cdc

@@ -180,7 +180,7 @@ access(all) contract NFTProviderAggregator {
 
         /// Borrow the collection of an NFT located in one of multiple collections through iterating over each collection
         ///
-        access(all) view fun borrowNFTCollection(id: UInt64): &{NonFungibleToken.Provider, NonFungibleToken.CollectionPublic} {
+        access(all) view fun borrowNFTCollection(id: UInt64): &{NonFungibleToken.Provider, NonFungibleToken.CollectionPublic}? {
             for collectionUUID in self.nftProviderCapabilities.keys {
                 // Check capabilities can still be borrowed since a NFT provider capability may pass the
                 // pre-condition checks at the time of being added with the addNFTWithdrawCapability method but
@@ -204,7 +204,7 @@ access(all) contract NFTProviderAggregator {
                     }
                 }
             }
-            panic("missing NFT")
+            return nil
         }
 
         /// Withdraw an NFT located in one of multiple collections through iterating over each collection
@@ -215,8 +215,8 @@ access(all) contract NFTProviderAggregator {
 
         /// Borrow an NFT located in one of multiple collections through iterating over each collection
         ///
-        access(all) view fun borrowNFT(id: UInt64): &{NonFungibleToken.NFT} {
-            return self.borrowNFTCollection(id: id).borrowNFT(id)!
+        access(all) view fun borrowNFT(id: UInt64): &{NonFungibleToken.NFT}? {
+            return self.borrowNFTCollection(id: id)?.borrowNFT(id) ?? nil
         }
 
         /// Create and return a Supplier resource

nft-provider-aggregator/scripts/aggregator_borrow_nft.cdc

@@ -0,0 +1,16 @@
+import NFTProviderAggregator from "NFTProviderAggregator"
+import NonFungibleToken from "NonFungibleToken"
+
+// Tries to borrow an NFT by ID from the Aggregator resource stored in `address`.
+// Returns the NFT's Type identifier if found, nil otherwise.
+
+access(all) fun main(address: Address, nftID: UInt64): &{NonFungibleToken.NFT}? {
+    let account = getAuthAccount<auth(BorrowValue) &Account>(address)
+
+    let aggregator = account.storage.borrow<&NFTProviderAggregator.Aggregator>(
+        from: NFTProviderAggregator.AggregatorStoragePath
+    ) ?? panic("Aggregator resource not found at ".concat(NFTProviderAggregator.AggregatorStoragePath.toString()))
+
+    let nft = aggregator.borrowNFT(id: nftID)
+    return nft
+}