code: private void ensureValueMode() throws IOException {
      switch (this.mode) {
        case MODE_START_LINE: {
          changeMode(MODE_VALUES);
          for (final Extra e : extras) {
            e.onBeforeFirstValue(this);
          }
          writeIndent();
          this.write(this.prefixFirtValueAtLine);
        }
        break;
        case MODE_COMMENTS: {
          this.BR();
          writeIndent();
          changeMode(MODE_VALUES);
          for (final Extra e : extras) {
            e.onBeforeFirstValue(this);
          }
          this.write(this.prefixFirtValueAtLine);
        }
        break;
        case MODE_VALUES:
          break;
        default:
          throw new Error("Unexpected state");
      }
    }
docs: Ensure the value mode.
  
  @throws IOException it will be thrown for transport errors