LWC Superbadge Challenge 8 - HandleSave() error

Hello, can anybody help me out here? Stuck at this since 2 days!!

<template>
  <lightning-tabset variant="scoped">
    <lightning-tab label="Gallery">
      <template if:true={boats.data}>
        <div class="slds-scrollable_y">
          <lightning-layout horizontal-align="center" multiple-rows>
            <template for:each={boats.data} for:item="boat">
              <lightning-layout-item
                key={boat.Id}
                padding="around-small"
                size="12"
                small-device-size="6"
                medium-device-size="4"
                large-device-size="3"
              >
                <c-boat-tile
                  boat={boat}
                  selected-boat-id={selectedBoatId}
                  onboatselect={updateSelectedTile}
                ></c-boat-tile>
              </lightning-layout-item>
            </template>
          </lightning-layout>
        </div>
      </template>
    </lightning-tab>
    <lightning-tab label="Boat Editor">
      <!-- Scrollable div and lightning datatable go here -->
      <template if:true={boats.data}>
        <div class="slds-scrollable_y">
          <lightning-datatable
            key-field="Id"
            data={boats.data}
            columns={columns}
            onsave={handleSave}
            draft-values={draftValues}
            hide-checkbox-column
            show-row-number-column	
          >
          </lightning-datatable>
        </div>
      </template>
    </lightning-tab>
    <lightning-tab label="Boats Near Me">
      <!-- boatsNearMe component goes here -->
      <c-boats-near-me boat-type-id={boatTypeId}></c-boats-near-me>
    </lightning-tab>
  </lightning-tabset>
</template>

import { LightningElement, wire, api, track } from 'lwc';
import getBoats from '@salesforce/apex/BoatDataService.getBoats';
import { updateRecord } from 'lightning/uiRecordApi';
import { ShowToastEvent } from 'lightning/platformShowToastEvent';
import { refreshApex } from '@salesforce/apex';
import { publish, MessageContext } from 'lightning/messageService';
import BOATMC from '@salesforce/messageChannel/BoatMessageChannel__c';
const LOADING_EVENT = 'loading';
const DONE_LOADING_EVENT = 'doneloading';
export default class BoatSearchResults extends LightningElement {
    boatTypeId = '';
    @track boats;
    @track draftValues = [];
    selectedBoatId = '';
    isLoading = false;
    error = undefined;
    wiredBoatsResult;
    @wire(MessageContext) messageContext;
    columns = [
        { label: 'Name', fieldName: 'Name', type: 'text', editable: 'true'  },
        { label: 'Length', fieldName: 'Length__c', type: 'number', editable: 'true' },
        { label: 'Price', fieldName: 'Price__c', type: 'currency', editable: 'true' },
        { label: 'Description', fieldName: 'Description__c', type: 'text', editable: 'true' }
    ];
    @api
    searchBoats(boatTypeId) {
        this.isLoading = true;
        this.notifyLoading(this.isLoading);
        this.boatTypeId = boatTypeId;
    }
    @wire(getBoats, { boatTypeId: '$boatTypeId' })
    wiredBoats(result) {
        this.boats = result;
        if (result.error) {
            this.error = result.error;
            this.boats = undefined;
        } else if (result.data) {
            //this.boats = result.data;
        }
        this.isLoading = false;
        this.notifyLoading(this.isLoading);
    }
    updateSelectedTile(event) {
        this.selectedBoatId = event.detail.boatId;
        this.sendMessageService(this.selectedBoatId);
    }
    handleSave(event) {
        const recordInputs = event.detail.draftValues.slice().map(draft => {
            const fields = Object.assign({}, draft);
            return { fields };
        });
        const promises = recordInputs.map(recordInput => updateRecord(recordInput));
        Promise.all(promises)
            .then(() => {
                this.showToastEvent('Success','Ship It!','success');
                return this.refresh();
            })
            .catch( error => {
                this.error = error;
                this.showToastEvent('Error', error.body.message, 'error');
            }).finally(() => {
                this.draftValues = [];
            });
    }
    @api
    async refresh() {
        this.isLoading = true;
        this.notifyLoading(this.isLoading);      
        await refreshApex(this.boats);
        this.isLoading = false;
        this.notifyLoading(this.isLoading);        
    }
    notifyLoading(isLoading) {
        var spinnerEvent;
        if (isLoading) {
            spinnerEvent = new CustomEvent(LOADING_EVENT);
        } else {
            spinnerEvent = new CustomEvent(DONE_LOADING_EVENT);
        }
        this.dispatchEvent(spinnerEvent);
    }
    showToastEvent(title, message, variant) {
        const toastEvent = new ShowToastEvent({
            title : title,
            message : message,
            variant : variant
        });
        this.dispatchEvent(toastEvent);
    }
    sendMessageService(selectedBoatId) { 
        publish(this.messageContext, BOATMC, { recordId : selectedBoatId });
    }
}

The functionality seems to be working fine, any help is appreciated.

Thank you!