alibaba/Sentinel · error · IllegalArgumentException

Null method

Error message

Null method

What it means

MethodUtil.resolveMethodName(Method) builds and caches the 'className:name:paramTypes' signature string used for method-level (Sphu.entry with Method) resource names. A null Method has no declaring class or name, so it throws IllegalArgumentException immediately.

Source

Thrown at sentinel-core/src/main/java/com/alibaba/csp/sentinel/util/MethodUtil.java:41

 * Util class for processing {@link Method}.
 *
 * @author youji.zj
 */
public final class MethodUtil {

    private static final Map<Method, String> methodNameMap = new ConcurrentHashMap<Method, String>();

    private static final Object LOCK = new Object();

    /**
     * Parse and resolve the method name, then cache to the map.
     *
     * @param method method instance
     * @return resolved method name
     */
    public static String resolveMethodName(Method method) {
        if (method == null) {
            throw new IllegalArgumentException("Null method");
        }
        String methodName = methodNameMap.get(method);
        if (methodName == null) {
            synchronized (LOCK) {
                methodName = methodNameMap.get(method);
                if (methodName == null) {
                    StringBuilder sb = new StringBuilder();

                    String className = method.getDeclaringClass().getName();
                    String name = method.getName();
                    Class<?>[] params = method.getParameterTypes();
                    sb.append(className).append(":").append(name);
                    sb.append("(");

                    int paramPos = 0;
                    for (Class<?> clazz : params) {
                        sb.append(clazz.getCanonicalName());
                        if (++paramPos < params.length) {

View on GitHub (pinned to a3f40ba8e9)

Solutions

1. Ensure the Method object passed in is non-null; log it before calling resolveMethodName.
2. If it comes from reflection, check why the lookup returned null (wrong method name, params mismatch, accessibility) and fix the lookup.
3. Guard: if (method == null) fall back to a string resource name instead of calling resolveMethodName.

Example fix

// before
Method m = clazz.getMethod("handle"); // may throw / be null after catch
String name = MethodUtil.resolveMethodName(m);

// after
Method m = clazz.getMethod("handle");
String name = (m != null)
    ? MethodUtil.resolveMethodName(m)
    : "handle-fallback-resource";

if (method == null) {
    throw new IllegalStateException("method lookup failed for resource " + resourceName);
}
String mn = MethodUtil.resolveMethodName(method);

boolean isResolvableMethod(Method m) {
    return m != null;
}

When it happens

Trigger: MethodUtil.resolveMethodName(null), or passing a Method reference that came from a failed reflective lookup (Class.getMethod wrapped so null is returned on failure).

Common situations: Method-based resource definition (MethodResourceUtil / SentinelResourceAspect method entry) where the target method annotation lookup returned null — e.g. @SentinelResource on an overloaded/inherited method not found reflectively, or AOP proxies returning null from a custom method resolver.

Related errors

• ${name} is null
• Invalid map instance
• Request cannot be null
• Bad class metadata
• charset is not allowed to be null

AI-assisted analysis of alibaba/Sentinel@a3f40ba8e9 (2026-08-14). Data as JSON: /api/errors/b0b6aa8950845309. Report an issue: GitHub.