What causes "Cannot call createParameterObject() on {}" in FasterXML/jackson-databind?

If you need a creator-parameter any-setter, declare @JsonAnySetter on a Map-typed parameter of a @JsonCreator constructor/factory (the supported creator form).

FasterXML/jackson-databind · error · UnsupportedOperationException

Cannot call createParameterObject() on {}

Error message

Cannot call createParameterObject() on {}

What it means

Thrown by the base SettableAnyProperty.createParameterObject() — the default implementation is unsupported because field/method-based any-setters have no 'parameter object' to create. Only the creator-parameter-based subclass (a Map-typed @JsonAnySetter used as a @JsonCreator argument) supports it; calling it on any other variant throws UnsupportedOperationException.

Source

Thrown at src/main/java/tools/jackson/databind/deser/SettableAnyProperty.java:177

     *
     * @since 2.18.1
     */
    public boolean isFieldType() { return _setterIsField; }

    /**
     * Method called to check whether this property is method
     *
     * @return 2.18.2
     */
    public boolean isSetterType() { return _setter instanceof AnnotatedMethod; }

    /**
     * Create an instance of value to pass through Creator parameter.
     *
     * @since 2.18
     */
    public Object createParameterObject() {
        throw new UnsupportedOperationException("Cannot call createParameterObject() on " + getClass().getName());
    }

    /*
    /**********************************************************************
    /* Public API, deserialization
    /**********************************************************************
     */

    /**
     * Method called to deserialize appropriate value, given parser (and
     * context), and set it using appropriate method (a setter method).
     */
    public void deserializeAndSet(JsonParser p, DeserializationContext ctxt,
            Object instance, String propName)
        throws JacksonException
    {
        try {
            Object key = (_keyDeserializer == null) ? propName

View on GitHub (pinned to a50c7d2a1d)

Solutions

If you need a creator-parameter any-setter, declare @JsonAnySetter on a Map-typed parameter of a @JsonCreator constructor/factory (the supported creator form).
If using field/method @JsonAnySetter, don't rely on createParameterObject(); ensure the deserializer uses the per-key deserializeAndSet path.
Remove the conflicting @JsonCreator or realign it with the any-setter shape.
Avoid calling createParameterObject() from custom code unless you've confirmed the variant via isFieldType()/isSetterType().

Example fix

// before: field-based any-setter combined with a creator expecting a map -> mismatch
class Bag {
    private Map<String,Object> props = new HashMap<>();
    @JsonAnySetter public void add(String k, Object v){ props.put(k, v); }
    @JsonCreator public Bag(@JsonProperty("props") Map<String,Object> p){ ... }
}
// after: any-setter as a creator parameter (supported form)
class Bag {
    private final Map<String,Object> props;
    @JsonCreator public Bag(@JsonAnySetter Map<String,Object> props){ this.props = props; }
}

Defensive patterns

Strategy: validation

Validate before calling

if (anyProperty.isFieldType() || anyProperty.isSetterType()) {
    // field/method form: createParameterObject() is unsupported
    throw new UnsupportedOperationException(
        "createParameterObject() only valid for creator-parameter any-setters");
}
Object paramObj = anyProperty.createParameterObject();

Try / catch

try {
    return anyProperty.createParameterObject();
} catch (UnsupportedOperationException e) {
    // any-setter is field/method form; fall back to per-key deserializeAndSet
    return null;
}

Prevention

Keep @JsonAnySetter and @JsonCreator consistent: creator-parameter form (Map arg) OR field/method form — not mixed.
Don't call createParameterObject() on field/method any-setters; use deserializeAndSet per key.
When upgrading Jackson, re-test types that combine @JsonAnySetter with @JsonCreator.

When it happens

Trigger: A bean declares @JsonAnySetter on a field or a single-arg setter method (NOT a creator Map parameter), and the deserialization path or a direct caller invokes createParameterObject(). Usually surfaces as an internal mismatch when @JsonAnySetter is combined with @JsonCreator in an incompatible way.

Common situations: Mixing field/method @JsonAnySetter with a @JsonCreator whose signature implies a collect-any Map that doesn't exist; upgrading Jackson where any-setter/creator resolution changed; calling the API directly from custom deserialization code without checking the any-setter form.

Related errors

AI-assisted analysis of FasterXML/jackson-databind@a50c7d2a1d (2026-08-06). Data as JSON: /api/errors/d047d57dfe4779ee. Report an issue: GitHub.