src/main/java/com/arpnetworking/steno/Logger.java
static @Nullable String[] createKeysFromCollection(
            @Nullable final Collection<String> collection,
            @Nullable final String... keys) {
        if (isNullOrEmpty(keys)) {
            return collection == null ? null : collection.toArray(new String[collection.size()]);
        }
        if (isNullOrEmpty(collection)) {
            return keys;
        }
        final String[] combined = new String[collection.size() + keys.length];
        for (int i = 0; i < keys.length; ++i) {
            combined[i] = keys[i];
        }
        int i = 0;
        for (final String item : collection) {
            combined[keys.length + i++] = item;
        }
        return combined;
    }
static @Nullable String[] createKeysFromCollection(
            @Nullable final Collection<String> collection,
            @Nullable final String... keys) {
        if (isNullOrEmpty(keys)) {
            return collection == null ? null : collection.toArray(new String[collection.size()]);
        }
        if (isNullOrEmpty(collection)) {
            return keys;
        }
        final String[] combined = new String[collection.size() + keys.length];
        for (int i = 0; i < keys.length; ++i) {
            combined[i] = keys[i];
        }
        int i = 0;
        for (final String item : collection) {
            combined[keys.length + i++] = item;
        }
        return combined;
    }
/* package private