code: public WordBuilder<I> repeatAppend(int num, I symbol) {
          if (num == 0) {
              return this;
          }
  
          ensureAdditionalCapacity(num);
          if (symbol == null) {
              length += num;
          } else {
              for (int i = num; i > 0; i--) {
                  array[length++] = symbol;
              }
          }
          return this;
      }
docs: Appends {@code num} copies of a symbol to the contents of the internal storage.
  
  @param num
  the number of copies
  @param symbol
  the symbol
  
  @return {@code this}