code: def get_scales(self, aesthetic):
          
          bool_lst = self.find(aesthetic)
          try:
              idx = bool_lst.index(True)
              return self[idx]
          except ValueError:
              return None
docs: Return the scale for the aesthetic or None if there
          isn't one.
  
          These are the scales specified by the user e.g
              `ggplot() + scale_x_continuous()`
          or those added by default during the plot building
          process