title: FlowInputMappingException when mapping of object in Spring Webflow
body: <p>I am trying to follow the code for Spring Webflow from 'Spring in Action'. However, when I tried to run the application, I got the following error:</p>
  
  <pre><code>org.springframework.webflow.engine.FlowInputMappingException: Errors occurred during input mapping on startup of the 'pizza' flow; errors = [[RequiredError@13cb4078 mapping = order -&gt; flowScope.order, code = 'required', error = true, errorCause = [null], originalValue = [null], mappedValue = [null]]]
  </code></pre>
  
  <p>I believe the line that instantiates the order object in the following flow xml is responsible for the exception:</p>
  
  <pre><code>&lt;var name="order" class="com.mycompany.pizza.domain.Order" /&gt;
      &lt;subflow-state id="customer" subflow="customer-flow"&gt;
          &lt;input name="order" value="order"/&gt;
          &lt;transition on="customerReady" to="buildOrder" /&gt;
      &lt;/subflow-state&gt;
  </code></pre>
  
  <p>My subflow xml looks like this:</p>
  
  <p>
      </p>
  
  <pre><code>&lt;view-state id="welcome"&gt;
      &lt;transition on="phoneEntered" to="lookupCustomer" /&gt;
  &lt;/view-state&gt;
  
  &lt;action-state id="lookupCustomer"&gt;
      &lt;evaluate result="order.customer"
          expression="pizzaFlowActions.lookupCustomer(requestParameters.phoneNumber)" /&gt;
      &lt;transition to="registrationForm"
          on-exception="com.mycompany.pizza.service.CustomerNotFoundException" /&gt;
      &lt;transition to="customerReady" /&gt;
  &lt;/action-state&gt;
  </code></pre>
  
  <p>Hope there's someone who could point me at the right direction. Thanks!</p>