protected static void checkArgumentLength(Method method, int expected, String methodName) {
        if (!hasExpectedArgumentLength(method, expected)) {
            throw new IllegalArgumentException(
                    String.format("Method '%s' expected %d argument but got %d arguments", methodName, expected, method.getParameterTypes().length));
        }
    }
Returns a Multimap from fieldName Strings to their getter Methods.

It expects to be called only from TaskSerDe. Multimap is used inside org.embulk.config.
embulk-deps/src/main/java/org/embulk/deps/config/TaskInvocationHandler.java