public static CIKey internStaticKey(final String key) {
        if (key == null) {
            return null;
        } else if (key.isEmpty()) {
            return EMPTY_STRING;
        } else {
            return CIKeys.internCommonKey(key);
        }
    }
Create a {@link CIKey} that will be held as a static variable.
Only use this for commonly used static {@link CIKey} instances
as if the key is not already held in the map of common {@link CIKey}s
then it will be added.
<p>
Is null safe. If key is null, returns null.
</p>
stroom-util-shared/src/main/java/stroom/util/shared/string/CIKey.java