private static object CombineConfigValues( object a, object b ) {
    if( a.GetType() != b.GetType() ) {
        throw new ModHelpersException( "Mismatched config value types." );
    }
    if( a == null ) {
        return b;
    }
    if( b == null ) {
        return a;
    }
    if( !(b is ICollection) ) {
        return b;
    }

    Type collectionType = b.GetType();

    List<object> rawCombinedList = ( (ICollection)a ).Cast<object>().ToList();
    rawCombinedList.AddRange( ( (ICollection)b ).Cast<object>() );

    MethodInfo castMethod = rawCombinedList.GetType().GetMethod( "Cast" );
    castMethod = castMethod.MakeGenericMethod( collectionType.GenericTypeArguments );

    var typedCombinedCollection = (IEnumerable)castMethod.Invoke( rawCombinedList, new object[] { } );

    return Activator.CreateInstance( collectionType, new object[] { typedCombinedCollection } );
}