quarkusio/quarkus · error · IllegalArgumentException

Media type was null

Error message

Media type was null

What it means

MediaTypeHeaderDelegate.fromString requires a non-null string because the JAX-RS HeaderDelegate contract mandates throwing IllegalArgumentException when the input is null. There is no default media type to substitute, so null input is rejected immediately before parsing.

Solutions

1. Check the string for null before calling fromString and substitute a sensible default such as MediaType.APPLICATION_JSON or APPLICATION_OCTET_STREAM.
2. Treat a null header as 'not specified' in your protocol logic instead of converting it.
3. Catch IllegalArgumentException if null input is expected and handle it as an empty-media-type case.

Example fix

// before
MediaType mt = MediaType.valueOf(headerValue);
// after
MediaType mt = headerValue == null ? MediaType.APPLICATION_OCTET_STREAM : MediaType.valueOf(headerValue);

if (headerValue == null || headerValue.isBlank()) {
    // treat as 'no media type specified'
}

static boolean hasMediaType(String s) {
    return s != null && !s.isBlank();
}

try {
    return MediaTypeHeaderDelegate.INSTANCE.fromString(type);
} catch (IllegalArgumentException e) {
    return MediaType.APPLICATION_OCTET_STREAM; // default for null/invalid
}

When it happens

Trigger: Passing a null String to MediaTypeHeaderDelegate.fromString(null), or indirectly via RuntimeDelegate header conversion when a header value variable is null (e.g. an unset config property or missing request header fed to MediaType conversion).

Common situations: Reading a Content-Type/Accept header that is absent and passing it straight to conversion; @ConfigProperty or map lookups returning null; deserializing optional header values into MediaType without a null check.

Related errors

• Param was null
• Param was null
• Does not support fromString
• Failed to parse media type
• Malformed media type:

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/5f5ad9c8a8febae8. Report an issue: GitHub.

Appendix: source

Thrown at independent-projects/resteasy-reactive/common/runtime/src/main/java/org/jboss/resteasy/reactive/common/headers/MediaTypeHeaderDelegate.java:127

        } else {
            return new MediaType(major, subtype);
        }
    }

    public static boolean quoted(String str) {
        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);
            for (char q : quotedChars) {
                if (c == q)
                    return true;
            }
        }
        return false;
    }

    public MediaType fromString(String type) throws IllegalArgumentException {
        if (type == null)
            throw new IllegalArgumentException("Media type was null");
        return parse(type);
    }

    public String toString(MediaType o) {
        if (o == null)
            throw new IllegalArgumentException("Param was null");
        MediaType type = o;
        String result = reverseMap.get(type);
        if (result == null) {
            result = internalToString(type);
            final int size = reverseMap.size();
            if (size >= MAX_MT_CACHE_SIZE) {
                reverseMap.clear();
                map.clear();
            }
            reverseMap.put(type, result);
            map.put(result, type);
        }

View on GitHub (pinned to e1c734241f)