Make sure that C{builderNames} is a subset of the configured
        C{self.builderNames}, returning an empty list if not.  If
        C{builderNames} is empty, use C{self.builderNames}.

        @returns: list of builder names to build on

def filterBuilderList(self, builderNames):
        """
        Make sure that C{builderNames} is a subset of the configured
        C{self.builderNames}, returning an empty list if not.  If
        C{builderNames} is empty, use C{self.builderNames}.

        @returns: list of builder names to build on
        """

        # self.builderNames is the configured list of builders
        # available for try.  If the user supplies a list of builders,
        # it must be restricted to the configured list.  If not, build
        # on all of the configured builders.
        if builderNames:
            for b in builderNames:
                if b not in self.builderNames:
                    log.msg("%s got with builder %s" % (self, b))
                    log.msg(" but that wasn't in our list: %s"
                            % (self.builderNames,))
                    return []
        else:
            builderNames = self.builderNames
        return builderNames