using System;

using System.Collections.Generic;

using System.Collections.ObjectModel;

using System.Linq;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        var text = "[thing, fallback=]";

​

        var fallbacks = Regex.Matches(text, @"\[([^,\[\]]+),[ ]*fallback[ ]*=([^\]]*)\]", RegexOptions.IgnoreCase).Cast<Match>()

                .Where(d => d.Groups.Count == 3).Where(d => !d.Groups[1].Value.Trim().IsEmpty()).ToDictionarySafe(d => d.Groups[1].Value.Trim(), e => e.Groups[2].Value.Trim());

        foreach (var f in fallbacks) {

            Console.WriteLine($"key={f.Key} {f.Key.GetType()} isNull={f.Key == null}");

            Console.WriteLine($"value={f.Value} {f.Value.GetType()} isNull={f.Value == null}");

        }

    }

}

​

public static class StringExtensionMethods {

    public static bool IsEmpty(this string @string)

    {

        return string.IsNullOrEmpty(@string);

    }

}

​

public static partial class EnumerableExtensions {

    public static Dictionary<TKey, TElement> ToDictionarySafe<TKey, TElement, TSource>(

        this IEnumerable<TSource> list,

        Func<TSource, TKey> keySelector,

        Func<TSource, TElement> elementSelector)

    {

        Dictionary<TKey, TElement> result = new Dictionary<TKey, TElement>();

        foreach (TSource source in list)

        {

            result[keySelector(source)] = elementSelector(source);

        }

​

        return result;

    }

​

}

​