Build query string using URIBuilder

UriQueryStringBuilder.cs

    public class UriQueryStringBuilder : UriBuilder
    {
        private readonly IDictionary<string, string> _queryParameters;

        public UriQueryStringBuilder(string schemeName, string hostName, string path) : this(schemeName, hostName, path, null) { }

        public UriQueryStringBuilder(string schemeName, string hostName, string path, IEnumerable<KeyValuePair<string, string>> queryParameters) : this(schemeName, hostName,path,null)
        {
            if (queryParameters == null) return;

            foreach (KeyValuePair<string,string> item in queryParameters)
            {
                AddQueryParameter(item.Key, item.Value);
            }
        }
        
        public UriQueryStringBuilder(string schemeName, string hostName, string path, IDictionary<string, string> queryParameters) : base(schemeName, hostName)
        {
            _queryParameters = queryParameters ?? new Dictionary<string,string>();
            Path = path;
        }

        public IDictionary<string, string> QueryParameters => _queryParameters;

        public void AddQueryParameter(string key, string value)
        {
            if (key == null) throw new ArgumentNullException(nameof(key));

            if (_queryParameters.ContainsKey(key)) throw new ArgumentException("An element with the same key already exists",nameof(key));

            _queryParameters.Add(key, value ?? string.Empty);
        }

        public override string ToString()
        {
            var query = new StringBuilder();
            foreach (var item in _queryParameters.Keys)
            {
                query.Append($"{item}={Uri.EscapeUriString(_queryParameters[item])}&");
            }

            if (query.Length > 0)
            {
                query.Length--; //Trim last character '&'
                Query = query.ToString();
            }
            return base.ToString();
        }
    }