attempt to understand entry

src/entry.rs

@@ -84,7 +84,8 @@ fn add_transaction_data(hash_data: &mut Vec<u8>, tx: &Transaction) {
 
 /// Creates the hash `num_hashes` after `start_hash`. If the transaction contains
 /// a signature, the final hash will be a hash of both the previous ID and
-/// the signature.
+/// the signature.  If num_hashes is zero and there's no transaction data,
+//  start_hash is  returned.
 pub fn next_hash(start_hash: &Hash, num_hashes: u64, transactions: &[Transaction]) -> Hash {
     let mut id = *start_hash;
     for _ in 1..num_hashes {
@@ -174,5 +175,10 @@ mod tests {
         let tick = next_entry(&zero, 1, vec![]);
         assert_eq!(tick.num_hashes, 1);
         assert_ne!(tick.id, zero);
+
+        let tick = next_entry(&zero, 0, vec![]);
+        assert_eq!(tick.num_hashes, 0);
+        assert_eq!(tick.id, zero);
+
     }
 }