when edit record i get error on function editemp

Problem

When click button edit on employee list it not open page or form of edit  and show error 

ERROR TypeError: Cannot read property 'toString' of undefined
    at EmployeeListComponent.push../src/app/employeelist.component.ts.EmployeeListComponent.editEmp (employeelist.component.ts:35)
this is error on line localStorage.setItem('editEmpId', employee.EmployeeId.toString()); 

on employeelist.component.ts i have function editemp as following

editEmp(employee: Employee): void {  
   localStorage.removeItem('editEmpId'); 
    console.log(employee.EmployeeId) ;
    localStorage.setItem('editEmpId', employee.EmployeeId.toString());  
    this.router.navigate(['employees']);
  }  

on employeelist.component.html

<tr *ngFor = "let emp of employees"><td> {{emp.employeeId}}</td><td> {{emp.branchCode}}</td><td> {{emp.employeeName}}</td><td><button (click)="editEmp(emp.employeeId)" class="btn btn-sm btn-outline-danger">Edit</button></td>

and this form employees.component.ts

import { Component } from '@angular/core'
import { ApiService } from './api.service'
import { NgForm } from '@angular/forms';
import { ToastrService } from 'ngx-toastr';
import { FormBuilder, FormGroup, Validators } from "@angular/forms";
import { Router } from "@angular/router"; 
@Component({
    selector :'employees',
    templateUrl : './employees.component.html'
})
export class EmployeesComponent{
    employees = {}
    empformlabel: string = 'Add Employee';  
    empformbtn: string = 'Save';
    constructor(private formBuilder: FormBuilder ,private router: Router , private api:ApiService,private toastr: ToastrService){}
    addForm: FormGroup; 
    btnvisibility: boolean = true; 
    ngOnInit() {
      this.addForm = this.formBuilder.group({  
        EmployeeId: [],  
        EmployeeName: ['', Validators.required],  
        JoinDate: ['', [Validators.required, Validators.maxLength(20)]], 
        BirthDate: ['', [Validators.required, Validators.maxLength(20)]], 
        EmployeeAge: ['', [Validators.required, Validators.maxLength(3)]],
        BranchCode: ['', [Validators.required, Validators.maxLength(2)]],
        Active: ['', Validators.required]  
      }); 
        //this.resetForm();
       let empid = localStorage.getItem('editEmpId');  
    if (+empid > 0) {  
      this.api.getEmployeeById( +empid).subscribe(data => {  
        this.addForm.patchValue(data);  
      })  
    }  
    this.btnvisibility = false;  
    this.empformlabel = 'Edit Employee';  
    this.empformbtn = 'Update';
      }


}

How to solve this error please ?