Joining strings while ignoring empty or null values

JoinStrings.cs

public static string JoinStrings(IEnumerable<string> args, string separator)
{
    var needsSeparator = false;
    var builder = new StringBuilder();
    foreach (var arg in args)
    {
        if (string.IsNullOrWhiteSpace(arg))
        {
            continue;
        }
        
        if (needsSeparator)
        {
            builder.Append(separator);
        }

        builder.Append(arg);
        needsSeparator = true;
    }

    return builder.ToString();
}