diff --git a/python/notamon_viewer/app.py b/python/notamon_viewer/app.py
index 96a1051..a5d6ae1 100644
--- a/python/notamon_viewer/app.py
+++ b/python/notamon_viewer/app.py
@@ -93,7 +93,7 @@ TEST_NOTAMON = Notamon(
                 species_name = 'Mudkip',
             )
 
-ADDRESS_NFTS = '02b82d36784146bd29415dbaa623a5f1cf6e6e1108'
+ADDRESS_NFTS = '02abbd5e40de91f4ab7f4a76f4b37b08de8f51bb2c'
 ADDRESS_ASSETS = '036080dc8a15e496e5b970f65112b4fe4ac022e62c'
 
 
@@ -135,7 +135,8 @@ def get_asset_variables(client, address) -> Iterator[AssetVariable]:
 
 
 def to_base64_png(b: bytes) -> str:
-    return f'data:image/png;base64,{base64.b64encode(b)}'
+    encoded = base64.b64encode(b).decode('utf8')
+    return f'data:image/png;base64,{encoded}'
 
 
 def get_notamon_nfts(client: pbc_client.PbcClient) -> Iterator[NotamonNFTData]:
diff --git a/rust/notamon-nft/src/upgrade.rs b/rust/notamon-nft/src/upgrade.rs
index 039bc1b..b51ec0d 100644
--- a/rust/notamon-nft/src/upgrade.rs
+++ b/rust/notamon-nft/src/upgrade.rs
@@ -22,6 +22,6 @@ pub fn is_upgrade_allowed(
 
 /// Upgrade contract state
 #[upgrade]
-pub fn upgrade_from_previous(_context: ContractContext, state: NFTContractState) -> NFTContractState {
+pub fn upgrade_from_previous(_context: ContractContext, mut state: NFTContractState) -> NFTContractState {
     state
 }