StdDelegatingSerializer does not consider a Converter that may return null for a non-null input

[plevart]

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Describe the bug

I have a custom NullModule extends SimpleModule that installs serializer and deserializer modifiers:

public NullModule() {
        setSerializerModifier(new NullSerializerModifier());
        setDeserializerModifier(new NullDeserializerModifier());
}

the NullSerializerModifier wraps each JsonSerializer with a subclass of StdDelegatingSerializer using a Converter that may return null for some special non-null instances of values to be serialized. I use this together with serializationInclusion(JsonInclude.Include.NON_NULL) configuration of ObjectMapper to suppress serialization of bean attributes with null values, but still allow selective serialization of JSON null values for attributes that are assigned these special non-null instancess (an alternative to JsonNullable wrapper class from openapi-tools but without ugly wrapper class). This works perfectly but recently I found a problem since I wanted to serialize a special instance of a type that represents a root of hierarchy of types for the first time. It works correctly for types that don't represent a hierarchy of types since in this case the following StdDelegatingSerializer method is invoked:

    public void serialize(Object value, JsonGenerator gen, SerializerProvider provider) throws IOException
    {
        Object delegateValue = convertValue(value);
        // should we accept nulls?
        if (delegateValue == null) {
            provider.defaultSerializeNull(gen);
            return;
        }
        // 02-Apr-2015, tatu: As per [databind#731] may need to do dynamic lookup
        JsonSerializer<Object> ser = _delegateSerializer;
        if (ser == null) {
            ser = _findSerializer(delegateValue, provider);
        }
        ser.serialize(delegateValue, gen, provider);
    }

As you can see, the value to be serialized is 1st converted to delegateValue via provided Converter and then a special case is considered when this converted value is null. In that case, null serialized value is emitted.

But in case the type of serialized value represents a hierarchy of types, the other StdDelegatingSerializer method is invoked:

    public void serializeWithType(Object value, JsonGenerator gen, SerializerProvider provider,
            TypeSerializer typeSer) throws IOException
    {
        // 03-Oct-2012, tatu: This is actually unlikely to work ok... but for now,
        //    let's give it a chance?
        Object delegateValue = convertValue(value);
        JsonSerializer<Object> ser = _delegateSerializer;
        if (ser == null) {
            ser = _findSerializer(value, provider);
        }
        ser.serializeWithType(delegateValue, gen, provider, typeSer);
    }

This method, OTOH, does not consider a special case that delegateValue might be null which causes a NullPointerException to be thrown later when this null value is attempted to be used for extracting the type ID from.

Currently my work-around is to override method serializeWithType in my custom StdDelegatingSerializer subclass and reimplement it with this special-case check inserted exactly at the same place as in the serialize method above.

Would you consider this a bug?

Regards, Peter

Version Information

2.17.0

Reproduction

Can be reproduced by running a unit test provided in the fix without the actual fix applied. The following is printed:

[ERROR] com.fasterxml.jackson.databind.ser.TestCustomSerializers.testIssue4575 -- Time elapsed: 0.005 s <<< ERROR!
com.fasterxml.jackson.databind.JsonMappingException: Cannot invoke "Object.getClass()" because "value" is null
        at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._wrapAsIOE(DefaultSerializerProvider.java:531)
        at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:504)
        at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:341)
        at com.fasterxml.jackson.databind.ObjectMapper._writeValueAndClose(ObjectMapper.java:4811)
        at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:4052)
        at com.fasterxml.jackson.databind.ser.TestCustomSerializers.testIssue4575(TestCustomSerializers.java:397)
        at java.base/java.lang.reflect.Method.invoke(Method.java:580)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
Caused by: java.lang.NullPointerException: Cannot invoke "Object.getClass()" because "value" is null
        at com.fasterxml.jackson.databind.jsontype.impl.TypeNameIdResolver.idFromValue(TypeNameIdResolver.java:115)
        at com.fasterxml.jackson.databind.jsontype.impl.TypeSerializerBase.idFromValue(TypeSerializerBase.java:92)
        at com.fasterxml.jackson.databind.jsontype.impl.TypeSerializerBase._generateTypeId(TypeSerializerBase.java:77)
        at com.fasterxml.jackson.databind.jsontype.impl.TypeSerializerBase.writeTypePrefix(TypeSerializerBase.java:45)
        at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeWithType(BeanSerializerBase.java:648)
        at com.fasterxml.jackson.databind.ser.std.StdDelegatingSerializer.serializeWithType(StdDelegatingSerializer.java:186)
        at com.fasterxml.jackson.databind.ser.impl.TypeWrappedSerializer.serialize(TypeWrappedSerializer.java:32)
        at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:502)
        ... 7 more

Expected behavior

I would expect the StdDelegatingSerializer to behave consistently for types that do and types that don't represent a type hierarchy.

Additional context

No response