Support empty commit. (#872)

crates/prover/src/core/vcs/prover.rs

@@ -38,7 +38,11 @@ impl<B: MerkleOps<H>, H: MerkleHasher> MerkleProver<B, H> {
     ///
     /// A new instance of `MerkleProver` with the committed layers.
     pub fn commit(columns: Vec<&Col<B, BaseField>>) -> Self {
-        assert!(!columns.is_empty());
+        if columns.is_empty() {
+            return Self {
+                layers: vec![B::commit_on_layer(0, None, &[])],
+            };
+        }
 
         let columns = &mut columns
             .into_iter()

crates/prover/src/core/vcs/verifier.rs

@@ -56,7 +56,9 @@ impl<H: MerkleHasher> MerkleVerifier<H> {
         queried_values: ColumnVec<Vec<BaseField>>,
         decommitment: MerkleDecommitment<H>,
     ) -> Result<(), MerkleVerificationError> {
-        let max_log_size = self.column_log_sizes.iter().max().copied().unwrap_or(0);
+        let Some(max_log_size) = self.column_log_sizes.iter().max() else {
+            return Ok(());
+        };
 
         // Prepare read buffers.
         let mut queried_values_by_layer = self
@@ -74,7 +76,7 @@ impl<H: MerkleHasher> MerkleVerifier<H> {
         let mut column_witness = decommitment.column_witness.into_iter();
 
         let mut last_layer_hashes: Option<Vec<(usize, H::Hash)>> = None;
-        for layer_log_size in (0..=max_log_size).rev() {
+        for layer_log_size in (0..=*max_log_size).rev() {
             // Prepare read buffer for queried values to the current layer.
             let mut layer_queried_values = queried_values_by_layer
                 .peek_take_while(|(log_size, _)| *log_size == layer_log_size)