in src/node_template.rs [106:115]
fn verify_padding_node(
node: &<Self as ProofExtractable>::ProofNode,
proof: &Self::PaddingProof,
_idx: &TreeIndex,
) -> bool {
let mut hasher = D::new();
hasher.update(PADDING_STRING.as_bytes());
hasher.update(&proof.hash);
*node == HashNodeSmt::<D>::new(hasher.finalize().to_vec())
}