I am trying to learn about Angular2's reactive forms by making a contact form. It all works good but there's an error that seems to give me quite some trouble. Everything works just fine when I use Validators.required but as soon as I add Validators.minLength or anything else on one of the controls everything messes up and I get this error in the browser's console: Expected validator to return Promise or Observable.. I looked around but I couldn't really find a simple explanation/ Here's my component:

export class ContactRouteComponent {
contactForm: FormGroup;
reasons = REASONS;

constructor(private fb: FormBuilder) {
    this.createForm();
}

createForm() {
    this.contactForm = this.fb.group({
        name: ['', <any>Validators.required, <any>Validators.minLength(3)],
        email: ['', <any>Validators.required],
        reason: ['',<any>Validators.required],
        message: ['', <any>Validators.required]
    });

    // AFISEAZA MESAJE EROARE
    this.contactForm.valueChanges.subscribe(data => this.onValueChanged(data));
    this.onValueChanged();
}

onSubmit() {
    console.log(this.prepareContactForm());
    this.contactForm.reset();
}

prepareContactForm() {
    const formModel = this.contactForm.value;

    const contactValues: Contact = {
        name: formModel.name as string,
        email: formModel.email as string,
        reason: formModel.reason as string,
        message: formModel.message as string
    };

    return contactValues;
}

onValueChanged(data?: any) {
    if(!this.contactForm) { return; }
    const form = this.contactForm;

    for(const field in this.formErrors) {
        // clear previous messages
        this.formErrors[field] = '';
        const control = form.get(field);

        if(control && control.dirty && !control.valid) {
            const messages = this.validationMessages[field];
            for(const key in control.errors) {
                this.formErrors[field] += messages[key] + ' ';
            }
        }
    }
}

formErrors = {
    'name': '',
    'email': '',
    'reason': '',
    'message': ''
}

validationMessages = {
    'name': {
        'required': 'Name is required',
        'minLength': 'Name has to be...'
    },
    'email': {
        'required': 'Name is required'
    },
    'reason': {
        'required': 'Name is required'
    },
    'message': {
        'required': 'Name is required'
    }
}

}