来自订阅的未定义的错误处理- Apollo和Angular 2

import { Component, OnInit } from '@angular/core';
import { Apollo } from 'apollo-angular';
import { catchError } from 'rxjs/operators';
import { of } from 'rxjs';

@Component({
  selector: 'app-example',
  templateUrl: './example.component.html',
  styleUrls: ['./example.component.css']
})
export class ExampleComponent implements OnInit {
  data: any;
  error: any;

  constructor(private apollo: Apollo) { }

  ngOnInit() {
    this.apollo
      .query({ query: YOUR_QUERY })
      .pipe(
        catchError(error => {
          this.error = error;
          return of(null); // 返回一个备用的数据流
        })
      )
      .subscribe(result => {
        if (result) {
          this.data = result.data;
        }
      });
  }
}