docs: 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