How do I write the aspect code that will work on a method with a optional parameter?

The code below works if MyService.getFacilities() has either no parameters or one database parameter. But if the parameter is database=null, then the aspect code is not called.

I am new to aop, so any comments on the code below is helpful.

Code:
////////////////////////////////////////////////////////////////////////////////
// <myapp>\grails-app\service\offload\MyService.groovy

package offload

class MyService {
	@Auditable
	def getFacilities(database=null) {
		// query database & return list
	}
}

///////////////////////////////////////////////////////////////////////////////
// <myapp>\grails-app\conf\spring\resources.groovy

import org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator
 
// Place your Spring DSL code here
beans = {

    autoProxyCreator(AnnotationAwareAspectJAutoProxyCreator) {
        proxyTargetClass = true
    }

	auditableAspect(offload.AuditableAspect)

}

///////////////////////////////////////////////////////////////////////////////
// <myapp>\grails-app\utils\offload\Auditable.groovy

package offload

import java.lang.annotation.ElementType
import java.lang.annotation.Target
import java.lang.annotation.RetentionPolicy
import java.lang.annotation.Retention

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Auditable {
}


///////////////////////////////////////////////////////////////////////////////
// <myapp>\grails-app\utils\offload\AuditableAspect.groovy

package offload

import org.aspectj.lang.annotation.Aspect
import org.aspectj.lang.annotation.Around
import org.aspectj.lang.annotation.Pointcut
import org.aspectj.lang.ProceedingJoinPoint

@Aspect
class AuditableAspect {

	@Pointcut("@annotation(offload.Auditable)")
	public void auditableOperation() {
	}
    
	@Around("offload.AuditableAspect.auditableOperation()")
	public Object add(ProceedingJoinPoint jp) throws Throwable {
    	
		// time the method
		def start = System.currentTimeMillis()
		Object retVal = jp.proceed()
		def stop = System.currentTimeMillis()

		println "elapsed: ${stop-start}ms"

		retVal
	}

}

///////////////////////////////////////////////////////////////////////////////
Thanks,
Paul Woods