docs: def blank_stim(self,type=None,fill=0):
          '''Makes a blank version of stim. If a type is not given, returned as same type as current stim.
          If a column stim, will fill in blanks with ``fill``'''
          blank = copy.copy(self)
          blank.name = 'Blank'
          if type==None:
              type = self.type()
          if type=="column":
              num_reps = self.reps
              if num_reps==None:
                  if self.type()=="column":
                      self.read_file()
                      num_reps = len(self.column)
                  else:
                      nl.notify('Error: requested to return a blank column, but I can\'t figure out how many reps to make it!',level=nl.level.error)
              blank.column = [fill]*num_reps
              return blank
          if type=="times":
              blank.times = []
              return blank