code: public ConditionalRowMutation otherwise(@Nonnull Mutation mutation) {
      Preconditions.checkNotNull(mutation);
      builder.addAllFalseMutations(mutation.getMutations());
      return this;
    }
docs: Adds changes to be atomically applied to the specified row if the condition does not yields any
  cells when applied to the row.
  
  <p>Each {@code mutation} can specify multiple changes and the changes are accumulated each time
  this method is called. Mutations are applied in order, meaning that earlier mutations can be
  masked by later ones. Must contain at least one entry if {@link #then(Mutation)} is empty, and
  at most 100000.