Spring mvc jackson json serialization: null as empty string or ignore null

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationConfig;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.DefaultSerializerProvider;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;

import java.io.IOException;

@Configuration
public class JacksonSerializationConfig {

    @Bean
    public ObjectMapper jacksonObjectMapper() {
        ObjectMapper objectMapper = new ObjectMapper();
        DefaultSerializerProvider sp = new DefaultSerializerProvider.Impl();
        sp.setNullValueSerializer(new NullSerializer());
        objectMapper.setSerializerProvider(sp);
        // objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL); //uncomment if need to ignore null strings
        return objectMapper;
    }

    @Bean
    public MappingJackson2HttpMessageConverter jackson2Converter() {
        MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
        converter.setObjectMapper(jacksonObjectMapper());
        return converter;
    }

    @Bean
    public SerializationConfig serializationConfig() {
        return jacksonObjectMapper().getSerializationConfig();
    }

    // and NullSerializer can be something as simple as:
    public class NullSerializer extends JsonSerializer<Object> {
        public void serialize(Object value, JsonGenerator jgen,
                              SerializerProvider provider)
                throws IOException, JsonProcessingException {
            // any JSON value you want...
            jgen.writeString("");
        }
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:aop="http://www.springframework.org/schema/aop" xmlns="http://www.springframework.org/schema/beans"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
      http://www.springframework.org/schema/beans/spring-beans.xsd
      http://www.springframework.org/schema/mvc
      http://www.springframework.org/schema/mvc/spring-mvc.xsd
      http://www.springframework.org/schema/context
      http://www.springframework.org/schema/context/spring-context.xsd
      http://www.springframework.org/schema/context
      http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">

    <mvc:default-servlet-handler/>
    <mvc:annotation-driven>
        <mvc:message-converters register-defaults="true">
            <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
                <property name="objectMapper" ref="jacksonObjectMapper"/>
            </bean>
        </mvc:message-converters>
    </mvc:annotation-driven>
</beans>