fix: deserialization of null storage keys in AccessListItem (#955)

* fix: deserialization of null storage keys in AccessListItem

* test: add test

* misc: apply review suggestions

* Update crates/eips/src/eip2930.rs

Co-authored-by: Matthias Seitz <matthias.seitz@outlook.de>

* misc: apply review suggestion

---------

Co-authored-by: Matthias Seitz <matthias.seitz@outlook.de>

crates/eips/src/eip2930.rs

@@ -30,6 +30,8 @@ pub struct AccessListItem {
             strategy = "proptest::collection::vec(proptest::arbitrary::any::<B256>(), 0..=20)"
         )
     )]
+    // In JSON, we have to accept `null` for storage key, which is interpreted as an empty array.
+    #[cfg_attr(feature = "serde", serde(deserialize_with = "alloy_serde::null_as_default"))]
     pub storage_keys: Vec<B256>,
 }
 
@@ -166,8 +168,24 @@ pub struct AccessListWithGasUsed {
 
 #[cfg(all(test, feature = "serde"))]
 mod tests {
+    use serde_json::json;
+
     use super::*;
 
+    #[test]
+    fn access_list_null_storage_keys() {
+        let json = json!([
+            {
+                "address": "0x81b7bdd5b89c90b63f604fc7cdd17035cb939707",
+                "storageKeys": null,
+            }
+        ]);
+
+        let access_list = serde_json::from_value::<AccessList>(json).unwrap();
+        assert_eq!(access_list.len(), 1);
+        assert_eq!(access_list[0].storage_keys, Vec::<B256>::default());
+    }
+
     #[test]
     fn access_list_serde() {
         let list = AccessList(vec![

crates/serde/src/lib.rs

@@ -18,6 +18,9 @@ use serde::Serializer;
 mod bool;
 pub use self::bool::*;
 
+mod optional;
+pub use self::optional::*;
+
 #[cfg_attr(not(test), deprecated = "use `quantity::{self, opt, vec}` instead")]
 pub mod num;
 #[allow(deprecated)]

crates/serde/src/optional.rs

@@ -0,0 +1,13 @@
+//! Serde functions for encoding optional values.
+use serde::{Deserialize, Deserializer};
+
+/// For use with serde's `deserialize_with` on a sequence that must be
+/// deserialized as a single but optional (i.e. possibly `null`) value.
+pub fn null_as_default<'de, T, D>(deserializer: D) -> Result<T, D::Error>
+where
+    T: Deserialize<'de> + Default,
+    D: Deserializer<'de>,
+{
+    let s: Option<T> = Deserialize::deserialize(deserializer)?;
+    Ok(s.unwrap_or_default())
+}