The promise rejected with the reason "[object Array]".] { code: 'ERR_UNHANDLED_REJECTION' }

Question

This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "[object Array]".] {
code: 'ERR_UNHANDLED_REJECTION' }

const uuid = require("uuid").v4
const path = require("path")
const fs = require("fs")

class Prescriptions{
    constructor(title){
        this.title = title
        this.id = uuid()
    }

    toJson(){
        return{
            title: this.title,
            id: this.id
        }
    }

    async save(){
        const prescription = await Prescriptions.getAll()
        prescription.push(this.toJson())

        return new Promise((reject, resolve)=>{
            fs.writeFile(
                path.join(__dirname, "..", "data", "prescriptions.json"),
                JSON.stringify(prescription),
                (err) => {
                    if(err){
                        reject(err)
                    } else{
                        resolve(err)
                    }
                }
               )
        })
    }

    static getAll(){
        return new Promise((reject, resolve) =>{
            fs.readFile(
                path.join(__dirname, '..', 'data', 'prescriptions.json'),
                'utf-8',
                (err, content) =>{
                    if(err){
                        reject(err)
                    } else{
                        resolve(JSON.parse(content))
                    }
                }
            )
        })
    }
}

module.exports = Prescriptions