custom controller: validation errors on cancel

Hi there.

I can't figure out how to circumvent validation when clicking a cancel button on a Visualforce page that uses a custom controller.

The page has this button:

<apex:commandButton action="{!cancel}" value="Cancel"/>

And the cancel method in the controller does this:

public PageReference cancel() { System.debug('cancel()'); String accountId = ApexPages.currentPage().getParameters().get('AccountId'); return new PageReference(accountId); }

but I never see my debug. Instead I see all the required fields on the page with red boxes ("Error: You must enter a value"). Any help would be appreciated.

Thanks.