Null PEs

When fsl_sub for Grid Engine is configured to have no parallel environments then the command line parser crashes:

$ /usr/local/fsl_6.0.7.1/share/fsl/bin/fsl_sub --show_config
Traceback (most recent call last):
  File "/usr/local/fsl_6.0.7.1/bin/fsl_sub", line 10, in <module>
    sys.exit(main())
             ^^^^^^
  File "/usr/local/fsl_6.0.7.1/lib/python3.11/site-packages/fsl_sub/cmdline.py", line 852, in main
    cmd_parser = build_parser(
                 ^^^^^^^^^^^^^
  File "/usr/local/fsl_6.0.7.1/lib/python3.11/site-packages/fsl_sub/cmdline.py", line 478, in build_parser
    pe_name=ll_envs[0])
            ~~~~~~~^^^
TypeError: 'NoneType' object is not subscriptable

Config snippet that causes this:

method: sge
method_opts:
    sge:
        affinity_type: Null
        large_job_split_pe: Null
queues:
    long.q:
        time: 99999999999
        max_size: 9999999999999
        slot_size: 9999999999999
        max_slots: 14