问访问嵌套对象属性时出错

EN

export interface adress{
city?: string;
neighborhood?: string; 
}


export interface programming{
backend?: string;
frontend?: string;
}

export interface nestedObject{
    firstName?: string;
    lastName?: string;
    completeAdress?: Array<adress>
    fullStackKnowledge?: Array<programming>
}


this.exple=[
      // first user 
      { 
        
        firstName: 'Msaddak',
        lastName: 'Rouabeh',
        
        
        completeAdress: [
          {
            city: 'Gafsa',
            neighborhood: 'Cité Hached Lalla',
          },
          {
            city: 'Monastir',
            neighborhood: 'Skanes',
          }
        ],
        fullStackKnowledge: [
          {
            backend: 'Express js',
            frontend: 'Angular',
          },
          {
            backend: 'Spring boot',
            frontend: 'React js',
          }
        ]
      },
      // Second user
      {
        firstName: 'Houssem',
        lastName: 'Ilahi',
        completeAdress: [
          {
            city: 'Tunis',
            neighborhood: 'Bardoo',
          },
          {
            city: 'Nabeul',
            neighborhood: 'Mrezka',
          }
        ],
        fullStackKnowledge: [
          {
            backend: '.net',
            frontend: 'Vue js',
          },
          {
            backend: 'Express js',
            frontend: 'React js',
          }
        ]
      }


    ]