"ServletRequest was null" warning in IdP 3.3.0

[Robert A Basch]

After upgrading one of our IdPs from 3.2.1 to 3.3.0, we started seeing
these warnings in the log on SAML 2 SSO requests, both apparently on
the incoming request, and when the response is being issued:

[line wrapped for readability]
WARN [net.shibboleth.idp.profile.config.AbstractProfileConfiguration:285] -
  ProfileConfiguration http://shibboleth.net/ns/profiles/saml2/sso/browser:
  ServletRequest was null

The IdP seems to be functioning properly, though; at least SPs are happily
consuming the resulting assertions.  Can anyone provide info as to what the
warning means, and advise as to what might be causing it?

Thanks,
Bob