TreeWalker WIP.

cas-core/src/error.rs

@@ -84,6 +84,9 @@ pub enum Error {
     #[error("io error: {0}")]
     IoError(#[from] std::io::Error),
 
+    #[error("non-unicode file name: '{0}'")]
+    NonUnicodeFileName(String),
+
     #[error("{0}")]
     UnknownError(String),
 }

cas-core/src/object_id.rs

@@ -57,6 +57,14 @@ impl FromStr for ObjectId {
     }
 }
 
+impl Default for ObjectId {
+    fn default() -> Self {
+        return Self {
+            id: Arc::new(vec![]),
+        }
+    }
+}
+
 impl fmt::Display for ObjectId {
     fn fmt(&self, f: &mut fmt::Formatter) -> std::result::Result<(), fmt::Error> {
         write_hex(f, self.id.as_slice())