(TypeError: Cannot read property 'length' of null at HttpHeaders.applyUpdate) Angular 5, Http Client

Don't set Null value in Header

I faced this kind of issue. The problem was in header, I was pushing null value i.e.

cloned = req.clone({
    headers: req.headers.append('token', token) // token is null
})

to fix this, I check token before setting into header i.e.

if (token) {
    cloned = req.clone({
        headers: req.headers.append('token', token)
    })
}

try like this :

service.ts

login(credentials): Observable<any> {
    return this.http.post("http://localhost:3000/api/Users/login", {
        username: credentials.username,
        password: credentials.password
    }).map(data => data.json())
}

component.ts

onLogin(credentials) {
    this.userService.login(credentials)
        .subscribe(data => {
            console.log('data', data);
        }, (error) => {
            console.log('error', error);
        })
}