how to fix the error "ERROR TypeError: Cannot read property '0' of undefined"

i am developing a catalog application, and i would like to display tooltips in my list options.

here is my list for you to understand better:

I want that when for example my mouse slides on the first option of the list the following message is displayed: "Exporte les données des catalogues du contexte de mapping en cours au format XML"

and so on ....

to do this i created this table in my .ts file :

const info_bulle_export: Array<{id:number, text:string}> =[

    {id:1, text:'Exporte les données des catalogues du contexte de mapping en cours au format XML'},
    {id:2, text:''},
    {id:3, text:'Exporte les données de mapping du contexte de mapping en cours au format XML'},
    {id:4, text:''},
    {id:5, text:'Exporte un rapport détaillé du mapping des scopes du contexte de mapping en cours au format XLS'},
    {id:6, text:'Exporte dans le même fichier XML les données catalogues et mapping par système de mapping, peut exporter dans une archive de fichiers XML tous les systèmes de mapping du contexte en cours'},
    {id:7, text:'Exporte le contexte de mapping en cours au format zip archivant les données catalogues dans un fichier XML et les données mapping dans un autre fichier XML'},
    {id:8, text:'Exporte les entités non mappées au format XLS'},
    {id:9, text:'Exporte les entités sans relations au format XLS'},
    {id:10, text:''}
];

and in my .html file I put this:

<option *ngFor="let worker of workerExportList; index as i" [ngValue]="worker" data-toggle="tooltip" data-placement="top" title="{{info_bulle_export[i]}}">{{worker.label}}</option>

here is all the code for my .ts file if you needed to:

import { Observable } from 'rxjs/Rx';
import { Http, RequestOptions, Headers, ResponseContentType, Response } from '@angular/http';
import { environment } from './../../../../environments/environment';
import { ExportService } from './../../exportDirectoryBrowsing/export.service';
import { sideMenuComponent } from './../../../layout/side-menu-component/side-menu.component';
import { WorkerParameterInfo } from './../workerParameterInfo';
import { WorkerExport } from './WorkerExport';
import { MappingSystemService } from './../../mappingSystem/mapping-system.service';
import { CatalogService } from './../../catalogue/Catalog.service';
import { Catalog } from './../../catalogue/Catalog';
import { MappingSystem } from './../../mappingSystem/MappingSystem';
import { MappingContext } from './../../mappingContext/MappingContext';
import { Component,  ViewChild } from '@angular/core';
import { LazyLoadEvent, ConfirmationService, TreeNode, Message } from 'primeng/primeng';
import { FormsModule } from '@angular/forms';
import { WorkersService } from '../worker.service';
import { SharedService } from './../../../shared.service';
import { FormGroup, FormBuilder } from '@angular/forms';
import * as FileSaver from 'file-saver';
import { DialogModule, Dialog } from 'primeng/components/dialog/dialog';
import {ProgressSpinnerModule} from 'primeng/components/progressspinner/progressspinner';
import { Timeouts } from 'selenium-webdriver';
import { $$iterator } from 'rxjs/internal/symbol/iterator';

const info_bulle_export: Array<{id:number, text:string}> =[

    {id:1, text:'Exporte les données des catalogues du contexte de mapping en cours au format XML'},
    {id:2, text:''},
    {id:3, text:'Exporte les données de mapping du contexte de mapping en cours au format XML'},
    {id:4, text:''},
    {id:5, text:'Exporte un rapport détaillé du mapping des scopes du contexte de mapping en cours au format XLS'},
    {id:6, text:'Exporte dans le même fichier XML les données catalogues et mapping par système de mapping, peut exporter dans une archive de fichiers XML tous les systèmes de mapping du contexte en cours'},
    {id:7, text:'Exporte le contexte de mapping en cours au format zip archivant les données catalogues dans un fichier XML et les données mapping dans un autre fichier XML'},
    {id:8, text:'Exporte les entités non mappées au format XLS'},
    {id:9, text:'Exporte les entités sans relations au format XLS'},
    {id:10, text:''}
];
@Component({
    selector: 'export',
    templateUrl: './export.component.html',
    styleUrls: ['./../../global.css'],
    providers: [WorkersService, ConfirmationService]
})
export class ExportComponent {
    value = 0;
    workerForm: FormGroup;
    selectedExportWorker: WorkerExport;
    selectedMappingContext: MappingContext;
    selectedMappingSystem: MappingSystem;
    selectedCatalog: Catalog;
    catalogues: Catalog[] = [];
    workerExportList: WorkerExport[] = [];
    mappingSystems: MappingSystem[] = [];
    blankObject: Catalog = new Catalog(0, 'TOUS', 'TOUS', null);
    blankObjectMS: MappingSystem = new MappingSystem(0, 'TOUS', null, null, null, null, null);
    blanckObjectMSAllInAZip : MappingSystem = new MappingSystem(100, 'TOUS DANS UN ZIP', null, null, null, null, null);
    isHiddenCatalogue = false;
    isHiddenMappingSystem = false;
    filesTree2: TreeNode[] = [];
    selectedFile: TreeNode;
    msgs: Message[] = [];
    display: Boolean = false;
    response: Response;

    @ViewChild('dialog') dialog: DialogModule;
    @ViewChild('spinner') spinner: ProgressSpinnerModule;

    constructor(private workersService: WorkersService, private api: SharedService,
        fb: FormBuilder, private catalogService: CatalogService, private mappingSystemService: MappingSystemService,
        private exportService: ExportService, private confirmationService: ConfirmationService, private http: Http) {

        this.workerExportList.push(new WorkerExport('catalogueExport', 'Export des catalogues'));
        this.workerExportList.push(new WorkerExport('mappingExportV1_0', 'Export des mappings S1F0'));
        this.workerExportList.push(new WorkerExport('mappingExport', 'Export des mappings'));
        this.workerExportList.push(new WorkerExport('release', 'Livraison'));
        this.workerExportList.push(new WorkerExport('summaryExport', 'Export du rapport XLS - mapping des scopes'));
        this.workerExportList.push(new WorkerExport('koalaExport', 'Export koala'));
        this.workerExportList.push(new WorkerExport('pamdaExport', 'Export pamda'));
        this.workerExportList.push(new WorkerExport('orphanExport', 'Export orphelins - entités non mappées'));
        this.workerExportList.push(new WorkerExport('hierarchyValidator', 'Validation hiérarchie - entités sans relation'));
        this.workerExportList.push(new WorkerExport('dataExport', 'Export des données'));

        this.workerForm = fb.group({
            'selectedExportWorker': '',
            'selectedCatalog': this.blankObject,
            'selectedMappingSystem': this.blankObjectMS
        })



        this.selectedCatalog = this.blankObject;
        this.selectedMappingSystem = this.blankObjectMS;

        this.api.getDataMappingContext().subscribe(_sharingData => {
            this.selectedMappingContext = _sharingData;
            if (_sharingData) {
                this.exportService.getByMappingCOntext(_sharingData.id).subscribe(data => {
                    this.createTree(data, this.filesTree2, null);
                    console.log(this.filesTree2);
                });
            }
        });
    }


    ngOnInit() {
        localStorage.removeItem('mapping');
        localStorage.removeItem('page');
        this.api.getDataMappingContext().subscribe(mappingContext => {
            if (mappingContext != null) {
                this.selectedMappingContext = mappingContext;
                this.mappingSystemService.getByMappingContext(this.selectedMappingContext.id).subscribe(data => this.mappingSystems = data);
                this.catalogService.getCatalogByMappingContext(this.selectedMappingContext.id).subscribe(data => this.catalogues = data);
            }
        });
    }

    exportCatalogue() {
       return this.workersService.exportCatalogue(new WorkerParameterInfo()).subscribe();
    }

    selectWorker() {
        this.value = 0;
        if (this.selectedExportWorker != null && (
            this.selectedExportWorker.code === 'catalogueExport' ||
            this.selectedExportWorker.code === 'dataExport')) {
            this.isHiddenCatalogue = false;
        } else {
            this.isHiddenCatalogue = true ;
        }

        if (this.selectedExportWorker != null && this.selectedExportWorker.code === 'koalaExport') {
            this.isHiddenMappingSystem = false;
        } else {
            this.isHiddenMappingSystem = true;
        }
    }

    executer() {
        this.value = 60;
        let workerParameterInfo = new WorkerParameterInfo();
        workerParameterInfo.currentMappingContext = this.selectedMappingContext.id;
        workerParameterInfo.disabledByUser = false;
        if (this.selectedExportWorker.code === 'catalogueExport') {
            this.display = true;
            workerParameterInfo.catalogueIdOrALL = this.selectedCatalog.id.toString();
            this.workersService.exportCatalogue(workerParameterInfo).subscribe((res: Response) => {
                console.log('response catalogueExport :', res);
                this.display = false;
                this.refresh();
            });
        } else if (this.selectedExportWorker.code === 'mappingExportV1_0') {
            this.display = true;
            this.workersService.exportMappingV10(workerParameterInfo).subscribe((res: Response) => {
                this.display = false;
                this.refresh();
            });
        } else if (this.selectedExportWorker.code === 'mappingExport') {
            this.display = true;
            this.workersService.exportMapping(workerParameterInfo).subscribe((res: Response) => {
                this.display = false;
                this.refresh();
            });
        } else if (this.selectedExportWorker.code === 'koalaExport') {
            this.display = true;
            workerParameterInfo.mappingSystemIdOrALL = this.selectedMappingSystem.id.toString();
            console.log('koala workerParameterInfo :', workerParameterInfo.mappingSystemIdOrALL);
            this.workersService.exportKoala(workerParameterInfo).subscribe((res: Response) => {
                console.log(res);
                this.display = false;
                this.refresh();
            });
        } else if (this.selectedExportWorker.code === 'release') {
            this.display = true;
            this.workersService.exportLivraison(workerParameterInfo).subscribe((res: Response) => {
                this.display = false;
                this.refresh();
            });
        } else if (this.selectedExportWorker.code === 'summaryExport') {
            this.display = true;
            this.workersService.exportSummary(workerParameterInfo).subscribe((res: Response) => {
                this.display = false;
                this.refresh();
            });
        } else if (this.selectedExportWorker.code === 'pamdaExport') {
            this.display = true;
            this.workersService.exportPamda(workerParameterInfo).subscribe((res: Response) => {
                this.display = false;
                this.refresh();
            });
        } else if (this.selectedExportWorker.code === 'orphanExport') {
            this.display = true;
            this.workersService.exportOrphan(workerParameterInfo).subscribe((res: Response) => {
                this.display = false;
                this.refresh();
            });
        } else if (this.selectedExportWorker.code === 'hierarchyValidator') {
            this.display = true;
            this.workersService.validateHierarchy(workerParameterInfo).subscribe((res: Response) => {
                this.display = false;
                this.refresh();
            });
        } else if (this.selectedExportWorker.code === 'dataExport') {
            this.display = true;
            workerParameterInfo.catalogueIdOrALL = this.selectedCatalog.id.toString();
            this.workersService.exportData(workerParameterInfo).subscribe((res: Response) => {
                this.display = false;
                this.refresh();
            });
        }
        this.value = 90;
        this.refresh();
        this.value = 100;
    }

    createTree(data: any[], tree: TreeNode[], parent: TreeNode) {
        // console.log('creating Tree From: ', data);

        data.forEach(dir => {
            let treeNode: TreeNode = {
                label: '',
                data: '',
                children: [],
                leaf: false,
                expandedIcon: '',
                collapsedIcon: '',
                icon: '',
                expanded: true,
                parent: {}
            };

            if (dir.leaf === false) {
                treeNode.label = dir.label;
                treeNode.expandedIcon = 'fa-folder-open';
                treeNode.collapsedIcon = 'fa-folder';
                treeNode.parent = parent;
                this.createTree(dir.children, treeNode.children, treeNode)
                tree.push(treeNode);
            } else {
                treeNode.label = dir.label;
                treeNode.leaf = true;
                treeNode.data = dir.data;
                treeNode.parent = parent;
                if (treeNode.label.endsWith('zip')) {
                    treeNode.icon = 'fa-file-archive';
                } else if (treeNode.label.endsWith('xml')) {
                    treeNode.icon = 'fa-file-code';
                } else if (treeNode.label.endsWith('xls')) {
                    treeNode.icon = 'fa-file-excel';
                } else if (treeNode.label.endsWith('txt')) {
                    treeNode.icon = 'fa-file';
                } else {
                    treeNode.icon = 'fa-file';
                }
                tree.push(treeNode);
            }
        });
    }


    confirmDelete() {
        this.confirmationService.confirm({
            message: 'Êtes-vous sûr de vouloir supprimer cet objet?',
            header: 'Confirmation de suppression',
            icon: 'fa fa-trash',
            accept: () => {
                this.deleteFile();
            }
        });
    }

    nodeSelect(event) {
        if (event.node.leaf === false) {
            this.selectedFile = null;
        }
    }

    deleteFile() {
        this.exportService.delete(this.selectedFile.data).subscribe(() => {
            this.selectedFile.parent.children.splice(this.selectedFile.parent.children.findIndex(
                child => child.data === this.selectedFile.data), 1);
            this.showSuccess('Fichier supprimé avec succès');
        });
    }


    downloadFile() {
        const headers = new Headers();
        headers.append('Content-Type', 'application/json');
        let requestOptions = new RequestOptions({
            headers: headers,
            responseType: ResponseContentType.Blob, // dont forget to import the enum
            // In case you get Module not found: Error: Can't resolve '@angular/http/src/enums', just use 3 instead ex 'responseType:3'
        });
        let workerParameterInfo = new WorkerParameterInfo();
        workerParameterInfo.pathFile = this.selectedFile.data;

        let bodyString = JSON.stringify(workerParameterInfo);
        this.http.post(`${environment.url.base}${environment.url.pamda.downloadFile}`, bodyString, requestOptions).subscribe(res => {
            FileSaver.saveAs(res.blob(), this.selectedFile.label)
        });

    }


    refresh() {
        this.filesTree2 = [];
        if (this.selectedMappingContext) {
            this.exportService.getByMappingCOntext(this.selectedMappingContext.id).subscribe(data => {
                this.createTree(data, this.filesTree2, null);
                // console.log(this.filesTree2);
            })
        }
    }

    showError() {
        this.msgs = [];
        this.msgs.push({ severity: 'error', summary: 'Message d\'erreur', detail: 'Vous ne pouvez pas supprimer ce catalogue' });
    }

    showSuccess(details) {
        this.msgs = [];
        this.msgs.push({ severity: 'success', summary: 'Succès', detail: details });
    }

}

and here is all the code for my .html file if you needed to:

 <div class="workers center">
    <p-dialog #dialog [(visible)]="display" modal="modal" width="450" responsive="true" closable="true" id="loading-panel" appendTo="body">
        <p-header style="color: #FB864F;font-size: 18px;">
            Worker en cours d'exécution ...
        </p-header>
        <img style="width: 200px; margin-left: 100px;" src="assets/images/panda_face.gif" />
    </p-dialog>
    <div class="box">
        <form [formGroup]="workerForm" id="workerForm">
            <div class="box-header with-border">
                <h1 class="box-title"> <i class="glyphicon glyphicon-th-large"></i> Workers </h1>
            </div>
            <div class="box-body">
                <div class="form-group">
                    <label for="worker" class="col-sm-2 control-label">Worker: </label>
                    <div class="col-sm-10">
                        <select id="worker" class="form-control" [(ngModel)]="selectedExportWorker" [formControl]="workerForm.controls['selectedExportWorker']"
                            (ngModelChange)="selectWorker()">
                            <option [ngValue]="blankObject"></option>
                            <option *ngFor="let worker of workerExportList; index as i" [ngValue]="worker" data-toggle="tooltip" data-placement="top" title="{{info_bulle_export[i]}}">{{worker.label}}</option>
                        </select>
                    </div>
                </div><br/><br/>
                <div class="form-group" [hidden]="isHiddenCatalogue">
                    <label for="catalog" class="col-sm-2 control-label">Catalogue: </label>
                    <div class="col-sm-10">
                        <select id="catalog" class="form-control" [(ngModel)]="selectedCatalog" [formControl]="workerForm.controls['selectedCatalog']">
                            <option [ngValue]="blankObject">{{blankObject.code}}</option>
                            <option *ngFor="let catalog of catalogues" [ngValue]="catalog">{{catalog.code}}</option>
                        </select>
                    </div>
                </div>
                <div class="form-group" [hidden]="isHiddenMappingSystem">
                    <label for="catalog" class="col-sm-2 control-label">Système de mapping: </label>
                    <div class="col-sm-10">
                        <select id="catalog" class="form-control" [(ngModel)]="selectedMappingSystem" [formControl]="workerForm.controls['selectedMappingSystem']">
                            <option [ngValue]="blankObjectMS">{{blankObjectMS.code}}</option>
                            <option [ngValue]="blanckObjectMSAllInAZip">{{blanckObjectMSAllInAZip.code}}</option>
                            <option *ngFor="let mappingSystem of mappingSystems" [ngValue]="mappingSystem">{{mappingSystem.code}}</option>
                        </select>
                    </div>
                </div>
            </div>
            <div class="box-footer form_settings">
                <button type="button" class="btn btn-info pull-right submit side" (click)="executer()">Executer</button>
            </div>
        </form>
    </div>

    <div class="box">
        <div class="box-header with-border">
            <h3 class="box-title"> <i class="glyphicon glyphicon-th-large"></i> Progression de l'exécution </h3>
        </div>
        <div class="box-body">
            <p-progressBar [value]="value"></p-progressBar>
            <div class="workerSuccess" id="workerSuccess"><h4>Le worker a été importé avec succès !</h4></div>
        </div>
    </div>

    <!-- <div class="box loading">
        <div class="box-header with-border">
            <h3 class="box-title"> <i class="glyphicon glyphicon-th-large"></i> Workers en cours d'exécution </h3>
        </div>
        <div class="box-body"></div>
    </div> -->

    <div class="box">
        <div class="box-header with-border">
            <h2 class="box-title"> <i class="glyphicon glyphicon-th-large"></i> Fichiers présents sur le serveur</h2>
        </div>
        <div class="PrimeTableDiv box-body">
            <p-toolbar>
                <div class="ui-toolbar-group-left form_settings toolbar">
                    <button pButton class="submit side toolbar" label="Supprimer" icon="fa-trash" (click)="confirmDelete()"></button>
                    <button pButton class="submit side toolbar" label="Télecharger" icon="fa-download" (click)="downloadFile()"></button>
                    <button pButton class="submit side toolbar" label="rafraichir" icon="fa-sync" (click)="refresh()"></button>
                </div>
            </p-toolbar>
            <!-- <p-tree [value]="filesTree2" selectionMode="single" [(selection)]="selectedFile" (onNodeSelect)="nodeSelect($event)" (onNodeUnselect)="nodeUnselect($event)" -->
            <p-tree [value]="filesTree2" selectionMode="single" [(selection)]="selectedFile" (onNodeSelect)="nodeSelect($event)"
                [style]="{'width':'100%'}">
                </p-tree>
        </div>
    </div>
</div>
<p-confirmDialog width="425" appendTo="body"></p-confirmDialog>

the problem is that i get the following error and i don't know how to fix it:

> ERROR TypeError: Cannot read property '0' of undefined
    at Object.eval [as updateRenderer] (ExportComponent.html:20)
    at Object.debugUpdateRenderer [as updateRenderer] (core.js:23937)
    at checkAndUpdateView (core.js:23312)
    at callViewAction (core.js:23548)
    at execEmbeddedViewsAction (core.js:23511)
    at checkAndUpdateView (core.js:23308)
    at callViewAction (core.js:23548)
    at execComponentViewsAction (core.js:23490)
    at checkAndUpdateView (core.js:23313)
    at callViewAction (core.js:23548)

I think the error comes from this line because when I remove it the error disappears but I don't know where the problem comes from exactly:

<option *ngFor="let worker of workerExportList; index as i" [ngValue]="worker" data-toggle="tooltip" data-placement="top" title="{{info_bulle_export[i]}}">{{worker.label}}</option>

can someone help me please?