Clarification needed in PAPE spec

[Allen Tom]

Another ambiguous parameter is the openid.pape.preferred_auth_policies 
request parameter in section 5.1.

The first sentence in Section 5.1 says that all the request parameters 
are mandatory (MUST be included), however the description  
openid.pape.preferred_auth_policies says that zero policies can be 
specified. Is there a special value for "zero policy"?  Or should the 
parameter be omitted if the no policy is requested?

http://openid.net/specs/openid-provider-authentication-policy-extension-1_0.html#anchor8

Thanks

Allen