title: Apache camel rest dsl RestBindingMode.json is not working
body: <p>I am trying to build rest api using camel-rest-dsl. I have tried with multiple provider, spark-rest, jetty. But it throwing marshelling exception when i use RestBindingMode.json, if i remove rest binding mode it works fine.</p>
  
  <p>SpringRouteBuilder</p>
  
  <pre><code>@Component
  public class RestAPIRoutes extends SpringRouteBuilder {
  
      @Override
      public void configure() throws Exception {
          restConfiguration().component("spark-rest")
              .bindingMode(RestBindingMode.json)
              .port(8787)
              .dataFormatProperty("prettyPrint","true");
  
          rest("/balance").produces("application/json").consumes("application/json")
              /* mock api */
              .get("/query").route().bean(BalanceService.class,"fetchBalance").endRest()
              /* fetch balance by msisdn*/
              .get("/query/{msisdn}").description("Fetch line balance by msisdn")
                  .type(BalanceInfo.class).to("bean:balanceService?method=fetchBalance(${header.msisdn})")
              .post("/update").type(BalanceInfo.class).outType(BalanceInfo.class).to("bean:balanceService?method=updateBalance");
  
      }
  
  }
  </code></pre>
  
  <p>Here balanceService is a simple Spring @Service with overloaded method and BalanceInfo is simple pojo class with two field and getter setters.</p>
  
  <h2>Pom Dependency</h2>
  
  <pre><code>    &lt;dependency&gt;
          &lt;groupId&gt;org.apache.camel&lt;/groupId&gt;
          &lt;artifactId&gt;camel-spark-rest&lt;/artifactId&gt;
          &lt;version&gt;2.22.1&lt;/version&gt;
      &lt;/dependency&gt;
  &lt;dependency&gt;
              &lt;groupId&gt;org.apache.camel&lt;/groupId&gt;
              &lt;artifactId&gt;camel-spring-boot-starter&lt;/artifactId&gt;
              &lt;version&gt;2.22.1&lt;/version&gt;
          &lt;/dependency&gt;
  </code></pre>
  
  <h2>Exception</h2>
  
  <pre><code>org.apache.camel.processor.binding.BindingException: Cannot bind to json as message body is not json compatible. Exchange[ID-LTB0202777-MAC-1540301942376-3-1]
      at org.apache.camel.processor.RestBindingAdvice.unmarshal(RestBindingAdvice.java:317) ~[camel-core-2.22.1.jar:2.22.1]
      at org.apache.camel.processor.RestBindingAdvice.before(RestBindingAdvice.java:137) ~[camel-core-2.22.1.jar:2.22.1]
  </code></pre>