code: public static void assertOneParameter(final Method method, Class<? extends Annotation> annotation)
     {
        if (method.getParameterTypes().length != 1)
        {
           throw annotation == null ? MESSAGES.methodHasToDeclareExactlyOneParameter(method) : MESSAGES.methodHasToDeclareExactlyOneParameter2(method, annotation);
        }
     }
docs: Asserts method have exactly one parameter.
  
  @param method to validate
  @param annotation annotation to propagate in exception message