title: How transform String in subflow route using spring integration dsl
body: <p>I coded a very simple example using route in spring integration with transform but is it giving <code>SpelEvaluationException</code>.</p>
  
  <p><strong>Code Gateway:</strong></p>
  
  <pre><code>@MessagingGateway
  @Component
  interface ApiGateway {
  
    @Gateway(requestChannel = "integrateAttributeChannel")
    fun integrateAttributes(message: String)
  
  }
  </code></pre>
  
  <p><strong>My flow:</strong></p>
  
  <pre><code>IntegrationFlows
              .from("integrateAttributeChannel")
              .route&lt;String, Boolean&gt;({ sellerId -&gt; sellerId.isBlank() },
                      { m -&gt;
                          m.subFlowMapping(true) { sf -&gt;
                              sf.transform&lt;String, String&gt; { t -&gt; t.toUpperCase() }
                          }
                          m.subFlowMapping(false) { sf -&gt;
                              sf.transform&lt;String, String&gt; { t -&gt; t.reversed() }
                          }
                      })
              .handle { t -&gt; println(t) }
              .get()
  </code></pre>
  
  <p><strong>Exception trace:</strong></p>
  
  <pre><code>Caused by: org.springframework.expression.spel.SpelEvaluationException: EL1004E: Method call: Method transform(java.lang.String) cannot be found on type br.com.gubee.config.AttributeFlow$flow$2$2$1
      at org.springframework.expression.spel.ast.MethodReference.findAccessorForMethod(MethodReference.java:225)
      at org.springframework.expression.spel.ast.MethodReference.getValueInternal(MethodReference.java:134)
      at org.springframework.expression.spel.ast.MethodReference.access$000(MethodReference.java:54)
      at org.springframework.expression.spel.ast.MethodReference$MethodValueRef.getValue(MethodReference.java:390)
      at org.springframework.expression.spel.ast.CompoundExpression.getValueInternal(CompoundExpression.java:90)
      at org.springframework.expression.spel.ast.SpelNodeImpl.getTypedValue(SpelNodeImpl.java:114)
      at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:365)
      at org.springframework.integration.util.AbstractExpressionEvaluator.evaluateExpression(AbstractExpressionEvaluator.java:172)
      at org.springframework.integration.util.AbstractExpressionEvaluator.evaluateExpression(AbstractExpressionEvaluator.java:160)
      at org.springframework.integration.handler.support.MessagingMethodInvokerHelper.invokeExpression(MessagingMethodInvokerHelper.java:664)
      at org.springframework.integration.handler.support.MessagingMethodInvokerHelper.invokeHandlerMethod(MessagingMethodInvokerHelper.java:655)
      at org.springframework.integration.handler.support.MessagingMethodInvokerHelper.processInternal(MessagingMethodInvokerHelper.java:491)
      at org.springframework.integration.handler.support.MessagingMethodInvokerHelper.process(MessagingMethodInvokerHelper.java:362)
      at org.springframework.integration.handler.MethodInvokingMessageProcessor.processMessage(MethodInvokingMessageProcessor.java:106)
      at org.springframework.integration.transformer.AbstractMessageProcessingTransformer.transform(AbstractMessageProcessingTransformer.java:113)
      at org.springframework.integration.transformer.MessageTransformingHandler.handleRequestMessage(MessageTransformingHandler.java:109)
      at org.springframework.integration.handler.AbstractReplyProducingMessageHandler.handleMessageInternal(AbstractReplyProducingMessageHandler.java:123)
      at org.springframework.integration.handler.AbstractMessageHandler.handleMessage(AbstractMessageHandler.java:162)
      at org.springframework.integration.dispatcher.AbstractDispatcher.tryOptimizedDispatch(AbstractDispatcher.java:115)
  </code></pre>