Object is possibly 'undefined' in ngif clause of angular 11

I have a service with the name “logManagerService”

import { Injectable } from '@angular/core';

@Injectable({
  // this line code make this service as singleton.
  providedIn: 'root'
})

export class logManagerService {
  private ErrorMessages:string[];

  constructor() {
    this.ErrorMessages=[];
   }

 public getErrorMassages():string[]{
    return this.ErrorMessages;
  }
}

in the component “display-log.component.html”, I want to display the content of “ErrorMessages” array. Although I use a question mark in order to check undefined in ngif clause, I get an error “Object is possibly 'undefined' “

<div *ngIf="**logManagerService?.getErrorMassages()?.length>0** " class="alert alert-danger"> 
        **<!--Object is possibly 'undefined'  -->**
    <h5>
        Errors
    </h5>
    <ul>
        <li *ngFor="let M of logManagerService.getErrorMassages()">
            {{M}}
        </li>
    </ul>
</div>

How can I fix it?

You can try this:

$any(logManagerService?.getErrorMassages())?.length > 0