title: WTForms can't seem to validate a SelectField box
body: <p>I've produced a select field for staff to choose their name.
  My goal for when the user does not select their name, but instead leaves the drop down box on the selection "---", In this scenario I want the ValidationError to then print it's message. At the moment nothing is printed when I test this. </p>
  
  <p>Here is my forms.py files:</p>
  
  <pre><code>from flask_wtf import Form
  from wtforms import StringField, BooleanField, SelectField
  from wtforms.validators import DataRequired, Required, ValidationError 
  
  class StaffNames(Form):
          staff = SelectField(
          'staff',
          choices=[("", "---"), ('1', 'John Jones'), ('2', 'Chris Hughes'), ('3', 'Lyn Fox')],
          )
          def validate_staff(form, field):
                  if field.data is "---":
                          raise ValidationError("Sorry, you havn't chosen a staff name")
  </code></pre>
  
  <p>Here is my view.py file:</p>
  
  <pre><code>from flask import render_template, flash, redirect
  from app import app
  from .forms import StaffNames
  
  @app.route('/')
  @app.route('/index', methods=['GET', 'POST'])
  def index():
      form = StaffNames()
      if form.validate_on_submit():
          return redirect('/results')
      return render_template('index.html',
                             title='RA Index Search',
                             form=form)
  </code></pre>
  
  <p>here is my index.html which relates to this form:</p>
  
  <pre><code>&lt;!-- extend base layout --&gt;
  {% extends "base.html" %}
  
  {% block content %}
  &lt;center&gt;
      &lt;h1&gt;Search&lt;/h1&gt;
      &lt;form action="" method="post" name="login"&gt;
  
          &lt;p&gt;{{ form.staff }} Select your name&lt;/p&gt;
          &lt;p&gt;&lt;input type="submit" value="Search"&gt;&lt;/p&gt;
      &lt;/form&gt;
  
  {% endblock %}
  </code></pre>
  
  <p>Can anyone see what I am doing wrong or suggest an alternative that won't melt my brain! lol
  Thanks</p>