fix: empty field casued an error

[Bugs5382]

When doing the unit testing for Bugs5382/node-hl7-server#21 there was an issue if the field was blank, it wasn't returning a "empty string"

const hl7_string: string = "MSH|^~\\&|||||20081231||ADT^A01^ADT_A01|12345||2.7\rEVN||20081231"

Caused an error:

async sendResponse (type: 'AA' | 'AR'): Promise<boolean> {
    try {
      this._ack = this._createAckMessage(type, this._message) // here because it could not find MSH 11.1 which in this string is empty
      this._socket.write(Buffer.from(`${VT}${this._ack.toString()}${FS}${CR}`))
    } catch (_e: any) {
      this._ack = this._createAEAckMessage()
      this._socket.write(Buffer.from(`${VT}${this._ack.toString()}${FS}${CR}`))
    }

    this._ackSent = true

    return this._ackSent
  }

[Bugs5382]

🎉 This issue has been resolved in version 1.0.0-beta.17 🎉

The release is available on:

• npm package (@develop dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[Bugs5382]

🎉 This issue has been resolved in version 1.0.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀