set (name, value, isLowerCase) {
    this.sortedMap = null
    const lowercaseName = isLowerCase ? name : name.toLowerCase()

    if (lowercaseName === 'set-cookie') {
      this.cookies = [value]
    }

    // 1. If list contains name, then set the value of
    //    the first such header to value and remove the
    //    others.
    // 2. Otherwise, append header (name, value) to list.
    this.headersMap.set(lowercaseName, { name, value })
  }
@see https://fetch.spec.whatwg.org/#concept-header-list-set
@param {string} name
@param {string} value
@param {boolean} isLowerCase