title: Custom object mapper not taking effect in springboot
body: <p>I've a springboot application. I'm trying to replace null values with a custom string ("NA"). So, I've configured an object mapper with a custom serializer provider that in turn has a custom null value serializer. You can check the code below.</p>
  
  <pre><code>@Configuration
  public class JacksonConfig {
      @Bean
      public ObjectMapper jacksonObjectMapper() {
          return new CustomObjectMapper();
      }
  
      @Bean
      public SerializationConfig serializationConfig() {
          return jacksonObjectMapper().getSerializationConfig();
      }
  }
  
  class CustomObjectMapper extends ObjectMapper {
      CustomObjectMapper() {
          super();
          DefaultSerializerProvider.Impl serializerProvider = new DefaultSerializerProvider.Impl();
          serializerProvider.setNullValueSerializer(new JsonSerializer&lt;Object&gt;() {
              @Override
              public void serialize(Object value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
                  gen.writeString("NA");
              }
          });
          this.setSerializerProvider(serializerProvider);
      }
  }
  </code></pre>
  
  <p>Now the problem is, even these beans are getting created, the custom null value serializer is still not taking effect. In the response, I'm still seeing lot of null values. Is there anything else I'm missing here?</p>