protected String convertKey(String key) {
        return key.toLowerCase(getLocale());
    }
Convert the given key to a case-insensitive key.
<p>The default implementation converts the key
to lower-case according to this Map's Locale.

@param key the user-specified key
@return the key to use for storing
see String#toLowerCase(Locale)
analyzer/src/main/java/nl/basjes/parse/useragent/utils/springframework/util/LinkedCaseInsensitiveMap.java