consensus: add cluster votes check

consensus/src/aggregator.rs

@@ -122,16 +122,17 @@ impl<V: StepVote> Aggregator<V> {
         // An committee member is allowed to vote only once per a single
         // step. Its vote has a weight value depending on how many times it
         // has been extracted in the sortition for this step.
-        let weight = cluster.add(signer, weight);
-        debug_assert!(weight.is_some());
+        let added = cluster
+            .add(signer, weight)
+            .expect("Vote to be added to cluster");
 
         let total = cluster.total_occurrences();
 
         debug!(
             event = "vote aggregated",
             ?vote,
             from = signer.to_bs58(),
-            added = weight,
+            added,
             total,
             majority = committee.majority_quorum(),
             super_majority = committee.super_majority_quorum(),

consensus/src/user/cluster.rs

@@ -24,6 +24,8 @@ where
     }
 
     /// Adds key with specified weight. Weight per key can be set only once.
+    ///
+    /// Return None if `weight` is 0 or key is already set.
     pub fn add(&mut self, key: &T, weight: usize) -> Option<usize> {
         if weight == 0 {
             return None;