Ошибка в коде - C# (180299)

brace = braceStack.Pop();

public static bool Check(string checkString)
        {
            var braceStack = new Stack();
 
            foreach (var chr in checkString)
            {
                if (chr == '(' || chr == '{' || chr == '[')
                {
                    braceStack.Push(chr);
                    continue;
                }
 
                if (chr != ')' && chr != '}' && chr != ']') continue;
 
                char brace;
 
                if (braceStack.Count > 0)
                    brace = braceStack.Pop();
                else
                    return false;
 
                switch (brace)
                {
                    case '(':
                        if (chr != ')') return false;
                        break;
                    case '{':
                        if (chr != '}') return false;
                        break;
                    case '[':
                        if (chr != ']') return false;
                        break;
                }
            }
 
            return braceStack.Count == 0;
        }