code: @Override
    public MutationResult execute() {
      if (pendingMutations == null || pendingMutations.isEmpty()) {
        return new MutationResultImpl(true, 0, null);
      }
      final BatchMutation<K> mutations = pendingMutations.makeCopy();
      pendingMutations = null;
      return new MutationResultImpl(keyspace.doExecuteOperation(new Operation<Void>(OperationType.WRITE) {
        @Override
        public Void execute(Cassandra.Client cassandra) throws Exception {
          cassandra.batch_mutate(mutations.getMutationMap(),
            ThriftConverter.consistencyLevel(consistencyLevelPolicy.get(operationType)));
          return null;
        }
      }));
  
    }
docs: Batch executes all mutations scheduled to this Mutator instance by addInsertion, addDeletion etc.
  May throw a HectorException which is a RuntimeException.
  @return A MutationResult holds the status.