map setup returns errors

[bnlawrence]

Version 3.3.0

Start cf-view, choose setup, choose map

With data already read:

Traceback (most recent call last):
  File "/Users/bnl28/Repositories/cf-view/cfview", line 2823, in menu
  self.map_window = Map_window(self.parent)
  File "/Users/bnl28/Repositories/cf-view/cfview", line 4581, in __init__
  self.initUI()
  File "/Users/bnl28/Repositories/cf-view/cfview", line 4667, in initUI
  if len(plotvars.fields) > 0:
  File "/Users/bnl28/Repositories/cf-view/cfview", line 4667, in initUI
  if len(plotvars.fields) > 0
     TypeError:  object of type 'NoneType' has no len()
     File read: ['/Users/bnl28/Data/mars-era-teaching2023.nc']

Before loading data same error without the File read ...