@ResponseBody가 null 객체 및 변수를 반환하지 않음

    
  <mvc:annotation-driven >
     <mvc:message-converters register-defaults="true">
     
     <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
           <property name="objectMapper">
               <bean class="com.fasterxml.jackson.databind.ObjectMapper">
                   <property name="serializationInclusion">
                      <value type="com.fasterxml.jackson.annotation.JsonInclude.Include">NON_NULLvalue>
                   property>
               bean>
          property>
        /bean>
    mvc:message-converters>
mvc:annotation-driven>