Client Undefined - Githubissues

Hi Lula, i had some problem when i refresh page on some component, it says Cannot read property 'call' of undefined

this is my App Module

//Other Module
import { NgxSoapModule } from 'ngx-soap';
@NgModule({
  declarations: [
    AppComponent,
  ],
  imports: [
    //Other Module
    NgxSoapModule,
  ],
  providers: [
    {

    }
  ],
  bootstrap: [AppComponent]
})
export class AppModule { }

this is my Component ts

import { Component, OnInit, AfterViewInit, ViewChild, OnDestroy } from '@angular/core';
import { FormBuilder, Validators } from '@angular/forms';
import { GeneralService } from 'src/app/_services/general.service';

@Component({
  selector: 'app-document',
  templateUrl: './document.component.html',
  styles: [
  ]
})
export class DocumentComponent implements OnInit {
  //Variable Declaring

  //Dependency Injection
  constructor(
    private fb : FormBuilder,
    private service : GeneralService,
  ) { }

  //Initialization
  ngOnInit(): void {
    console.log('fired OnInit');

    this.initializeList();
    this.resetFormData();
  }

  //Func
  get f() { return this.formData.controls; }

  //Func
  initializeList() : void {
   this.getCategoryList();
    this.getJobTitleList();
  }

  //Func
  getCategoryList(){
    this.service.GetCategoryList().subscribe(res=>{      
      this.categoryList = res.result.GetCategoryListResult.CategoryList;
    })
  }

  //Func
  getJobTitleList(){
    this.service.GetAllJobTitle().subscribe(res=>{
      this.jobTitleList = res.result.GetAllJobTitleResult.JobTitleVM;
    })
  }

and this is my Service

import { Injectable } from '@angular/core';
import { Client, ISoapMethodResponse, NgxSoapService } from 'ngx-soap';
import { Observable } from 'rxjs';
import { environment } from 'src/environments/environment';

@Injectable({
  providedIn: 'root'
})
export class GeneralService {
  client : Client;

  constructor(
    private soap : NgxSoapService
  ) {
   //this function always skipped only when i reload Document Component
    this.soap.createClient(environment.wsURL).then(client=>{
      client.addSoapHeader({
        'tns:ModuleCredential':{
          'tns:ModuleAppName':'xxxx',
          'tns:ModuleUserName':'xxxx',
          'tns:ModulePassword':'xxxx'
        }  
      });
      client.addHttpHeader(
        'Content-Type','text/xml; charset=utf-8'
      );
      this.client = client;
    })
    .catch(err=>console.log('SoapError',err))
   }

  GetCategoryList():Observable<ISoapMethodResponse>{
    const body ={
      data : null
    };
    return this.client.call('GetCategoryList',body);
  }

every time i refresh or reload page i've got this error

ERROR TypeError: Cannot read property 'call' of undefined
    at GeneralService.GetCategoryList (general.service.ts:44)
    at DocumentComponent.getCategoryList (document.component.ts:104)
    at DocumentComponent.initializeList (document.component.ts:91)
    at DocumentComponent.ngOnInit (document.component.ts:69)
    at callHook (core.js:4726)
    at callHooks (core.js:4690)
    at executeInitAndCheckHooks (core.js:4630)
    at refreshView (core.js:12026)
    at refreshEmbeddedViews (core.js:13404)
    at refreshView (core.js:12035)

the constructor always not triggered

lula / ngx-soap

Client Undefined #94