quarkusio/quarkus · warning · IllegalArgumentException

param was null

Error message

param was null

What it means

CacheControlDelegate.toString(CacheControl) serializes a CacheControl object into a Cache-Control header string. The JAX-RS HeaderDelegate contract mandates IllegalArgumentException when the object to serialize is null.

Source

Thrown at independent-projects/resteasy-reactive/common/runtime/src/main/java/org/jboss/resteasy/reactive/common/headers/CacheControlDelegate.java:84

            } else {
                if (val == null)
                    val = "";
                result.getCacheExtension().put(name, val);
            }
        }
        return result;
    }

    private static StringBuilder addDirective(String directive, StringBuilder buffer) {
        if (buffer.length() > 0)
            buffer.append(", ");
        buffer.append(directive);
        return buffer;
    }

    public String toString(CacheControl value) {
        if (value == null)
            throw new IllegalArgumentException("param was null");
        StringBuilder buffer = new StringBuilder();
        if (value.isNoCache()) {
            List<String> fields = value.getNoCacheFields();
            if (fields.size() < 1) {
                addDirective("no-cache", buffer);
            } else {
                for (String field : value.getNoCacheFields()) {
                    addDirective("no-cache", buffer).append("=\"").append(field).append("\"");
                }
            }
        }
        if (value instanceof ExtendedCacheControl) {
            ExtendedCacheControl ecc = (ExtendedCacheControl) value;
            if (ecc.isPublic()) {
                addDirective("public", buffer);
            }
        }
        if (value.isMustRevalidate())

View on GitHub (pinned to e1c734241f)

Solutions

1. Null-check the CacheControl before serializing and skip setting the header when null
2. Initialize a default CacheControl (e.g. new CacheControl()) instead of leaving null
3. Use Optional<CacheControl> and only write the header if present
4. Fix the code path that produces the null object

Example fix

// before
String header = CacheControlDelegate.INSTANCE.toString(cacheControl); // NPE-style failure on null
// after
if (cacheControl != null) {
    response.header("Cache-Control", CacheControlDelegate.INSTANCE.toString(cacheControl));
}

if (cacheControl == null) { /* skip setting header */ }

boolean isSerializable(CacheControl cc) { return cc != null; }

try {
    String h = CacheControlDelegate.INSTANCE.toString(cc);
} catch (IllegalArgumentException e) {
    // null CacheControl; omit header or substitute default
}

When it happens

Trigger: Passing a null CacheControl to CacheControlDelegate.INSTANCE.toString(null), e.g. when building a response header from a value that failed to initialize.

Common situations: Cache-control settings loaded from config that resolved to null; conditional header-building code that forgot the null case; unit tests exercising the delegate with null.

Related errors

• Param was null
• Param was null
• param was null
• value was null
• param was null

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/7d062e5501a9f804. Report an issue: GitHub.