Exception on filtering with a bad field name

[mafrosis]

> jira ls --filter 'epic-link = "CLDP-162"'
Traceback (most recent call last):
  File "/Users/mblack/Development/me/jira-offline/venv/bin/jira", line 33, in <module>
    sys.exit(load_entry_point('jira-offline', 'console_scripts', 'jira')())
  File "/Users/mblack/Development/me/jira-offline/venv/lib/python3.9/site-packages/click/core.py", line 1137, in __call__
    return self.main(*args, **kwargs)
  File "/Users/mblack/Development/me/jira-offline/venv/lib/python3.9/site-packages/click/core.py", line 1062, in main
    rv = self.invoke(ctx)
  File "/Users/mblack/Development/me/jira-offline/venv/lib/python3.9/site-packages/click/core.py", line 1668, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/mblack/Development/me/jira-offline/venv/lib/python3.9/site-packages/click/core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/mblack/Development/me/jira-offline/venv/lib/python3.9/site-packages/click/core.py", line 763, in invoke
    return __callback(*args, **kwargs)
  File "/Users/mblack/Development/me/jira-offline/venv/lib/python3.9/site-packages/click/decorators.py", line 26, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/Users/mblack/Development/me/jira-offline/jira_offline/cli/params.py", line 90, in wrapper
    return func(*args, **kwargs)
  File "/Users/mblack/Development/me/jira-offline/jira_offline/cli/params.py", line 114, in wrapper
    return func(*args, **kwargs)
  File "/Users/mblack/Development/me/jira-offline/jira_offline/cli/main.py", line 83, in cli_ls
    jira.df,
  File "/Users/mblack/Development/me/jira-offline/venv/lib/python3.9/site-packages/peak/util/proxies.py", line 12, in __getattribute__
    return getattr(subject,attr)
  File "/Users/mblack/Development/me/jira-offline/jira_offline/jira.py", line 102, in df
    return self.filter.apply()
  File "/Users/mblack/Development/me/jira-offline/jira_offline/sql_filter.py", line 103, in apply
    queried_columns = dict(gather_column_values(self._where))
  File "/Users/mblack/Development/me/jira-offline/jira_offline/sql_filter.py", line 99, in gather_column_values
    yield from gather_column_values(x)
  File "/Users/mblack/Development/me/jira-offline/jira_offline/sql_filter.py", line 96, in gather_column_values
    for v in where.values():
AttributeError: 'str' object has no attribute 'values'