code: private boolean isHandlerMethod(final Method method) {
          boolean isHandler = false;
  
          if (hasStartSagaAnnotation(method) || hasHandlerAnnotation(method)) {
              if (method.getReturnType().equals(Void.TYPE)) {
                  Class<?>[] parameterTypes = method.getParameterTypes();
                  if (parameterTypes.length == 1) {
                      isHandler = true;
                  } else {
                      LOG.warn("Method {}.{} marked for saga does not have the expected single parameter.", method.getDeclaringClass(), method.getName());
                  }
              } else {
                  LOG.warn("Method {}.{} marked for saga event handling but does return a value.", method.getDeclaringClass(), method.getName());
              }
          }
  
          return isHandler;
      }
docs: Checks whether method has expected annotation arguments as well as signature.