title: Display errors in v-for loop VueJs
body: <p>I try to display error for each field from a v-for. But I get an error " Cannot read property '$error' of undefined", and I am not sure why.</p>
  
  <pre><code>&lt;b-row  v-for="(v,index) in $v.years.$each.$iter" :key="index"&gt;
      &lt;b-col&gt;
          &lt;b-form-group&gt;
              &lt;b-form-select
                  v-model="v.year.$model"
                  :class="{
                      'is-invalid':$v.year.$error, 'is-valid':!$v.year.$invalid}"
              &gt;&lt;/b-form-select&gt;
              &lt;div class="invalid-feedback" v-if="!$v.year.required"&gt;This field is required!&lt;/div&gt;
          &lt;/b-form-group&gt;
      &lt;/b-col&gt;
  &lt;/b-row&gt;
  
  validations: {
      years:{
          $each:{
              year:{
                  required
              },
          },
      }
  },
  </code></pre>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>If I remove <code>year</code> from :class and v-if, it works, but if I have one error, It shows on each field, instead of just one.</p>