title: Angular-Formly - Access Model names for calculated fields with key names containing dot(.)
body: <p>I have a config json with 3 fields, the 3rd field being a calculated field from data in the previous 2 fields.
  Now the catch here is I have dot(.) in their key names. e.g. &quot;something.someone&quot;
  When I try rendering the form I get an error showing undefined.
  My config_json :</p>
  <pre><code>{
  &quot;fieldGroupClassName&quot;: &quot;row&quot;,
  &quot;fieldGroup&quot;: [
  {
              &quot;className&quot;: &quot;col-2&quot;,
              &quot;key&quot;: &quot;remarks_backflow.bed&quot;,
              &quot;type&quot;: &quot;input&quot;,
              &quot;templateOptions&quot;: {
                &quot;type&quot;: &quot;number&quot;,
                &quot;label&quot;: &quot;Bed&quot;,
                &quot;placeholder&quot;: &quot;&quot;,
                &quot;required&quot;: true
              }
            },
  {
              &quot;className&quot;: &quot;col-2&quot;,
              &quot;key&quot;: &quot;remarks_backflow.gas&quot;,
              &quot;type&quot;: &quot;input&quot;,
              &quot;templateOptions&quot;: {
                &quot;type&quot;: &quot;number&quot;,
                &quot;label&quot;: &quot;Gas&quot;,
                &quot;placeholder&quot;: &quot;&quot;,
                &quot;required&quot;: true
              }
            },
  {
              &quot;className&quot;: &quot;col-2&quot;,
              &quot;key&quot;: &quot;remarks_backflow.diff&quot;,
              &quot;type&quot;: &quot;input&quot;,
              &quot;templateOptions&quot;: {
                &quot;type&quot;: &quot;number&quot;,
                &quot;label&quot;: &quot;Difference&quot;,
                &quot;placeholder&quot;: &quot;&quot;,
                &quot;required&quot;: true
              },
              &quot;expressionProperties&quot;: {
                &quot;model['remarks_backflow.diff']&quot;:&quot;model['remarks_backflow.bed'] - model['remarks_backflow.gas']&quot;
              }
            },
  ]
  }
  </code></pre>
  <p>The error is :
  FormBuilderComponent.html:24 ERROR TypeError: [Formly Error] [Expression &quot;model['pushin_temperature.kiln_id']&quot;] Cannot set property 'kiln_id']' of undefined
  <a href="https://i.stack.imgur.com/by1P9.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/by1P9.jpg" alt="enter image description here" /></a></p>
  <p>Thanks in advance!</p>