Attempt to serialize SpecData - not working

SpecUtil

package tests

import com.fasterxml.jackson.annotation.JsonFilter
import com.fasterxml.jackson.core.JsonGenerator
import com.fasterxml.jackson.databind.JsonMappingException
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.databind.SerializationFeature
import com.fasterxml.jackson.databind.SerializerProvider
import com.fasterxml.jackson.databind.jsonFormatVisitors.JsonObjectFormatVisitor
import com.fasterxml.jackson.databind.node.ObjectNode
import com.fasterxml.jackson.databind.ser.FilterProvider
import com.fasterxml.jackson.databind.ser.PropertyFilter
import com.fasterxml.jackson.databind.ser.PropertyWriter
import com.fasterxml.jackson.databind.ser.impl.SimpleFilterProvider
import groovy.json.JsonBuilder

class SpecUtil {
    static String toPrettyString(def data) {
        new JsonBuilder(data).toPrettyString()
    }

    static String serialize(Object obj) {
        ObjectMapper mapper = new ObjectMapper()
        mapper.addMixIn(Object, DynamicMixIn)

        FilterProvider filters = new SimpleFilterProvider()
                .addFilter("dynamicFilter", new  MyPropertyFilter())
        mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false)

         return mapper.writer(filters).writeValueAsString(obj)
    }

    static toFile(Object obj) {
        new File('tmp.obj').withObjectOutputStream {
            it.writeObject(obj)
        }
    }

    @JsonFilter("dynamicFilter")
    static class DynamicMixIn {
    }

    static class MyPropertyFilter implements PropertyFilter {

        boolean shouldSerialize(PropertyWriter writer) {
            !(writer.name in ['metaclass', 'parent','specData','superSpec','subSpec','specsTopToBottom','specsBottomToTop','reflection','featureMethod','dataProviders'])

        }

        @Override
        void serializeAsField(Object pojo, JsonGenerator gen, SerializerProvider prov, PropertyWriter writer) throws Exception {
            if(shouldSerialize(writer)) {
                writer.serializeAsField(pojo, gen, prov)
            }
        }

        @Override
        void serializeAsElement(Object elementValue, JsonGenerator gen, SerializerProvider prov, PropertyWriter writer) throws Exception {
            if (shouldSerialize(writer)) {
                writer.serializeAsElement(pojo, gen, prov)
            }

        }

        @Override
        void depositSchemaProperty(PropertyWriter writer, ObjectNode propertiesNode, SerializerProvider provider) throws JsonMappingException {
            if (shouldSerialize(writer)) {
                writer.depositSchemaProperty(propertiesNode, provider)
            }

        }

        @Override
        void depositSchemaProperty(PropertyWriter writer, JsonObjectFormatVisitor objectVisitor, SerializerProvider provider) throws JsonMappingException {
            if (shouldSerialize(writer)) {
                writer.depositSchemaProperty(objectVisitor, provider)
            }

        }
    }

}