region_a.order_vars.avail() : Error occurs while searching available variables ATL10

[marionbocquet]

region_a = ipx.Query('ATL10',[-55, 50, 48, 71],['2019-02-22','2019-02-28'], start_time='00:00:00', end_time='23:59:59')
region_a.order_vars.avail()

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "packages/icepyx/venv/icepyx/lib/python3.9/site-packages/icepyx/core/variables.py", line 142, in avail
    self._avail = is2ref._get_custom_options(
  File "packages/icepyx/venv/icepyx/lib/python3.9/site-packages/icepyx/core/is2ref.py", line 116, in _get_custom_options
    format_vals.remove("")
ValueError: list.remove(x): x not in list

Same as for region_a.order_vars

[mfisher87]

I did a quick edit to format your code. Here's how I did it:

```python
region_a = ipx.Query('ATL10',[-55, 50, 48, 71],['2019-02-22','2019-02-28'], start_time='00:00:00', end_time='23:59:59')
region_a.order_vars.avail()
```

I'm able to reproduce this on my end. Definitely a bug!