src/main/java/com/arpnetworking/steno/Logger.java
static @Nullable  String[] createKeysFromArray(
            @Nullable final String[] array, 
            @Nullable final String... keys) {
        if (isNullOrEmpty(keys)) {
            return array;
        }
        if (isNullOrEmpty(array)) {
            return keys;
        }
        final String[] combined = Arrays.copyOf(keys, array.length + keys.length);
        for (int i = 0; i < array.length; ++i) {
            combined[keys.length + i] = array[i];
        }

        return combined;
    }
static @Nullable  String[] createKeysFromArray(
            @Nullable final String[] array, 
            @Nullable final String... keys) {
        if (isNullOrEmpty(keys)) {
            return array;
        }
        if (isNullOrEmpty(array)) {
            return keys;
        }
        final String[] combined = Arrays.copyOf(keys, array.length + keys.length);
        for (int i = 0; i < array.length; ++i) {
            combined[keys.length + i] = array[i];
        }

        return combined;
    }
/* package private