Fix FutureWarning
```
fontbakery/Lib/fontbakery/checkrunner.py:410: FutureWarning: The behavior of this method will change in future versions. Use specific 'len(elem)' or 'elem is not None' test instead.
if all(not x for x in args.values()):
```
@@ -407,7 +407,7 @@ class CheckRunner:
if inspect.isgenerator(v) or inspect.isgeneratorfunction(v):
args[k] = list(v)
- if all(not x for x in args.values()):
+ if all(x is None for x in args.values()):
status = (SKIP, "No applicable arguments")
return (status, None)
return None, args
