FasterXML/jackson-databind · error · IllegalArgumentException

Cannot pass null resolver

Error message

Cannot pass null resolver

What it means

Thrown by MapperBuilder.addAbstractTypeResolver when the supplied resolver is null. The builder treats null as a programming error rather than a silent no-op, because silently skipping it would mask a wiring bug in the caller.

Source

Thrown at src/main/java/tools/jackson/databind/cfg/MapperBuilder.java:1496

        return _this();
    }

    /**
     * Method that may be used to remove all {@link DeserializationProblemHandler}s added
     * to this builder (if any).
     */
    public B clearProblemHandlers() {
        _problemHandlers = null;
        return _this();
    }

    /**
     * Method for inserting specified {@link AbstractTypeResolver} as the first resolver
     * in chain of possibly multiple resolvers.
     */
    public B addAbstractTypeResolver(AbstractTypeResolver resolver) {
        if (resolver == null) {
            throw new IllegalArgumentException("Cannot pass null resolver");
        }
        _abstractTypeResolvers = ArrayBuilders.insertInListNoDup(_abstractTypeResolvers, resolver);
        return _this();
    }

    /*
    /**********************************************************************
    /* Changing settings, date/time
    /**********************************************************************
     */

    /**
     * Method for configuring the default {@link DateFormat} to use when serializing time
     * values as Strings, and deserializing from JSON Strings.
     * If you need per-request configuration, factory methods in
     * {@link ObjectReader} and {@link ObjectWriter} instead.
     */
    public B defaultDateFormat(DateFormat f) {

View on GitHub (pinned to a50c7d2a1d)

Solutions

1. Guard the call site: only register the resolver when you hold a non-null instance.
2. If the resolver is optional, wrap the call in `if (resolver != null)` or Objects.requireNonNull first.
3. Fix the upstream lookup/DI so a real resolver is produced.

Example fix

// before
builder.addAbstractTypeResolver(maybeResolver()); // maybeResolver() returns null -> throws
// after
AbstractTypeResolver resolver = maybeResolver();
if (resolver != null) {
    builder.addAbstractTypeResolver(resolver);
}

AbstractTypeResolver resolver = obtainResolver();
Objects.requireNonNull(resolver, "AbstractTypeResolver must not be null");
builder.addAbstractTypeResolver(resolver);

When it happens

Trigger: Calling mapperBuilder.addAbstractTypeResolver(null), or passing a lookup/DI result that resolved to null (e.g. Optional.orElse(null) or an unset bean).

Common situations: Conditional configuration where the resolver only sometimes exists; a refactor that left a null in place; a DI container failing to inject the bean; a feature flag disabling the resolver but not the registration call.

Related errors

• Cannot pass null Deserializers
• Cannot pass null KeyDeserializers
• Cannot pass null modifier
• Cannot pass null resolver
• AnnotationIntrospector returned Converter definition of type

AI-assisted analysis of FasterXML/jackson-databind@a50c7d2a1d (2026-08-06). Data as JSON: /api/errors/2e085288a1d36974. Report an issue: GitHub.