fix(mpt): Empty root node case (op-rs#705)

Author: clabby

Diff for: crates/mpt/src/node.rs

@@ -109,14 +109,15 @@ impl TrieNode {
     }
 
     /// Returns the commitment of a [TrieNode::Blinded] node, if `self` is of the
-    /// [TrieNode::Blinded] variant.
+    /// [TrieNode::Blinded] or [TrieNode::Empty] variants.
     ///
     /// ## Returns
     /// - `Some(B256)` - The commitment of the blinded node
     /// - `None` - `self` is not a [TrieNode::Blinded] node
     pub const fn blinded_commitment(&self) -> Option<B256> {
         match self {
             Self::Blinded { commitment } => Some(*commitment),
+            Self::Empty => Some(EMPTY_ROOT_HASH),
             _ => None,
         }
     }
@@ -681,6 +682,12 @@ mod test {
     use alloy_trie::{HashBuilder, Nibbles};
     use rand::prelude::SliceRandom;
 
+    #[test]
+    fn test_empty_blinded() {
+        let trie_node = TrieNode::Empty;
+        assert_eq!(trie_node.blinded_commitment().unwrap(), EMPTY_ROOT_HASH);
+    }
+
     #[test]
     fn test_decode_branch() {
         const BRANCH_RLP: [u8; 83] = hex!("f851a0eb08a66a94882454bec899d3e82952dcc918ba4b35a09a84acd98019aef4345080808080808080a05d87a81d9bbf5aee61a6bfeab3a5643347e2c751b36789d988a5b6b163d496518080808080808080");