oracle/graal · error · IllegalArgumentException

Expected a map.

Error message

Expected a map.

What it means

The tagged overload deserialize(json, proxyFactory, tag) requires the node to be an EconomicMap — unlike the untagged overload, it cannot pass through scalars because it has no way to attach type information to them. IllegalArgumentException('Expected a map.') fires when the JSON node at that position is a scalar/array where an object map was required.

Source

Thrown at compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replaycomp/JsonReplayCodec.java:1968

                    }
                    return deserializer.deserialize(map, this, proxyFactory);
                } else {
                    return json;
                }
            }

            @Override
            @SuppressWarnings("unchecked")
            public Object deserialize(Object json, CompilationProxies.ProxyFactory proxyFactory, String tag) throws DeserializationException {
                if (json instanceof EconomicMap<?, ?>) {
                    EconomicMap<String, Object> map = (EconomicMap<String, Object>) json;
                    ObjectSerializer deserializer = tagSerializers.get(tag);
                    if (deserializer == null) {
                        throw new IllegalArgumentException("No deserializer registered for tag " + tag);
                    }
                    return deserializer.deserialize(map, this, proxyFactory);
                } else {
                    throw new IllegalArgumentException("Expected a map.");
                }
            }

            private Architecture architecture;

            @Override
            public void setArchitecture(Architecture arch) {
                architecture = arch;
            }

            @Override
            public Architecture getArchitecture() {
                return architecture;
            }
        };
    }

    /**

View on GitHub (pinned to a66e9ccd1d)

Solutions

1. Inspect the replay file at the position indicated by the enclosing deserializer's context and restore the object node with its 'tag'
2. Re-record the file with the same build
3. If the value is legitimately a scalar, route it through the untagged deserialize overload instead

// Guard the node kind before the tagged call
if (!(json instanceof EconomicMap<?,?>)) {
    throw new IllegalArgumentException("Expected a tagged object node, got: " + json);
}

When it happens

Trigger: A tagged deserialization lands on a non-map node: file structure drifted (a field that used to be an object became a plain value), hand-edited JSON inlining a scalar where an object belongs, or a codec version change moving a field's shape.

Common situations: Manual JSON restructuring; version skew changing whether a value is boxed in an object with a tag or written inline; parser differences producing lists where maps are expected.

Related errors

• Unknown class ${className} for constant${value}
• The replay map does not contain a tag: ${map}
• Failed to serialize ${op} due to: ${cause}
• No singleton found for ${registration}
• Invalid marker type.

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/5448b00f946abb28. Report an issue: GitHub.