Problem

• when calculating gunning_fog for es, the call raises an exception due to the missing key syllable_threshold

Analysis

debugging reveals that the function might have been designed to work as:

• if there's a config value of that key, return that
• if there's no config value but a default value for that key, return that
• if there's neither value, throw!

but that's not how it works, and the function throws, even though the default config en exists.

Solution

If the logic is correct, here's the fix in this MR + the test to demonstrate. The logic is made somewhat more trivial.