title: Camunda: Cannot resolve identifier for an exclusive gateway
body: <p>I tried to use a html form for a user task in which a variable gets defined, to select a sequenzflow in the following exclusive gateway.
  html:</p>
  
  <pre><code>&lt;div class="form-group"&gt;
      &lt;div class="radiobutton"&gt;
          &lt;label&gt;
              &lt;input cam-variable-name="altneu" cam-variable-type="String" type="radio" name="altneu" class="form-control" value="NEU"/&gt;
              Neukunde
          &lt;/label&gt;
          &lt;label&gt;
              &lt;input cam-variable-name="altneu" cam-variable-type="String" type="radio" name="altneu" class="form-control" value="ALT"/&gt;
              Altkunde
          &lt;/label&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>Sequenceflows:</p>
  
  <pre><code>&lt;bpmn:sequenceFlow id="SequenceFlow_0a0vwxr" name="Kunden-stammdaten sind vorhanden" sourceRef="ExclusiveGateway_0vokx46" targetRef="ExclusiveGateway_074f3z1"&gt;
  &lt;bpmn:conditionExpression xsi:type="bpmn:tFormalExpression"&gt;&lt;![CDATA[${altneu == 'ALT'}]]&gt;&lt;/bpmn:conditionExpression&gt;
  &lt;/bpmn:sequenceFlow&gt;
  
  &lt;bpmn:sequenceFlow id="SequenceFlow_1cwjztj" name="Kundenstammdaten sind nicht vorhanden" sourceRef="ExclusiveGateway_0vokx46" targetRef="Task_1peelfz"&gt;
  &lt;bpmn:conditionExpression xsi:type="bpmn:tFormalExpression"&gt;&lt;![CDATA[${altneu == 'NEU'}]]&gt;&lt;/bpmn:conditionExpression&gt;
  &lt;/bpmn:sequenceFlow&gt;
  </code></pre>
  
  <p>I get this exception when executing:</p>
  
  <blockquote>
    <p>An error happend while submitting the task form :
    Cannot submit task form 713c798f-ebeb-11e7-9cb1-dcfe074be7ab: Unknown property used in expression: ${altneu == 'NEU'}. Cause: Cannot resolve identifier 'altneu'</p>
  </blockquote>