FasterXML/jackson-databind · error · IllegalArgumentException

Cannot pass null property name

Error message

Cannot pass null property name

What it means

BeanPropertyMap.findDefinition rejects a null property name with IllegalArgumentException. It is a construction-time lookup that does no case-insensitive matching or alias expansion, and a null key has no defined behavior, so it fails fast.

Solutions

1. Null-check the key before calling findDefinition; skip or use a sentinel instead.
2. Ensure all SettableBeanProperty instances have non-null names at construction.
3. If a name is genuinely optional, use an empty string rather than null.

Example fix

// before
SettableBeanProperty p = map.findDefinition(maybeNullName); // throws if null

// after
SettableBeanProperty p = (maybeNullName != null) ? map.findDefinition(maybeNullName) : null;

if (name == null) {
    throw new IllegalArgumentException("name required");
}
return map.findDefinition(name);

static boolean isNonEmptyName(String n) { return n != null && !n.isEmpty(); }

try { map.findDefinition(name); }
catch (IllegalArgumentException e) {
    if (e.getMessage().equals("Cannot pass null property name")) {
        // guard upstream against null names
    } else throw e;
}

When it happens

Trigger: Calling findDefinition(null) from custom factory/introspection code; a property whose getName() returns null being passed through; reflective code that strips names during property processing.

Common situations: Custom modules or mixins that produce a SettableBeanProperty with a null name; bugs in third-party libraries that call findDefinition with an unguarded external value; unit tests probing the map with arbitrary input.

Related errors

• deserialization problems (showing first 5):%n
• maxProblems must be positive, was
• No entry ' ' found, can't replace
• Trying to resolve a forward reference with id
• AnnotationIntrospector returned `Class<

AI-assisted analysis of FasterXML/jackson-databind@87876ca5c0 (2026-08-11). Data as JSON: /api/errors/a25c9a58a23ad66e. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/tools/jackson/databind/deser/bean/BeanPropertyMap.java:419

    public SettableBeanProperty findDefinition(int index)
    {
        for (SettableBeanProperty prop : _propsInOrder) {
            if ((prop != null) && (index == prop.getPropertyIndex())) {
                return prop;
            }
        }
        return null;
    }

    /**
     * NOTE: does NOT do case-insensitive matching -- only to be used during construction
     * and never during deserialization process -- nor alias expansion.
     */
    public SettableBeanProperty findDefinition(String key)
    {
        if (key == null) {
            throw new IllegalArgumentException("Cannot pass null property name");
        }
        for (SettableBeanProperty prop : _propsInOrder) {
            if (key.equals(prop.getName())) {
                return prop;
            }
        }
        return null;
    }

    /*
    /**********************************************************************
    /* Std method overrides
    /**********************************************************************
     */

    @Override
    public String toString()
    {

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