title: Property ' ' is used before its initialization
body: <p>I am following a youtube tutorial on how to consume a rest api in Angular Material table and am trying to apply it to my app. For some reason I get this error:</p>
  <pre><code>Property 'PERSONAL_DATA' is used before its initialization. 
  </code></pre>
  <p>This is my ts.file, what do I have to do? Im very new to angular</p>
  <pre><code>import { Component, OnInit } from '@angular/core';
  import { MatTableDataSource } from '@angular/material/table';
  import { Personal } from 'src/app/models/personal.model';
  import { PersonalService } from 'src/app/services/personal.service';
  
  @Component({
    selector: 'app-personal-list',
    templateUrl: './personal-list.component.html',
    styleUrls: ['./personal-list.component.css']
  })
  
  export class PersonalListComponent implements OnInit {
  
    PERSONAL_DATA? : Personal[]
    displayedColumns: string[] = ['name', 'age'];
    dataSource = new MatTableDataSource&lt;Personal&gt;(this.PERSONAL_DATA);
  
    constructor(private personalService: PersonalService) { }
  
    ngOnInit(): void {
      this.getAllPersonalTable();
    }
  
    private getAllPersonalTable(){
      let resp = this.personalService.getAllPersonal();
      resp.subscribe(report =&gt;this.dataSource.data=report as Personal[])
    }
  }
  </code></pre>