code: function parseBulkString (parser) {
    const length = parseLength(parser)
    if (length === undefined) {
      return
    }
    if (length < 0) {
      return null
    }
    const offset = parser.offset + length
    if (offset + 2 > parser.buffer.length) {
      parser.bigStrSize = offset + 2
      parser.totalChunkSize = parser.buffer.length
      parser.bufferCache.push(parser.buffer)
      return
    }
    const start = parser.offset
    parser.offset = offset + 2
    if (parser.optionReturnBuffers === true) {
      return parser.buffer.slice(start, offset)
    }
    return parser.buffer.toString('utf8', start, offset)
  }
docs: Parse a '$' redis bulk string response
  @param {JavascriptRedisParser} parser
  @returns {undefined|null|string}