If you run this code:
System.Collections.Specialized.NameValueCollection queryString = System.Web.HttpUtility.ParseQueryString("noKey&=emptyKey&A=Akey");
queryString will actually have the running type of System.Web.HttpValueCollection.
What's great about this class is that its ToString method output is the collection's content in a nice URL encoded format.
As with its base class (NameValueCollection), there’s a difference between a null string and an empty string key and the parsing treats query string parameters with no parameter specification as having a null string key and parameters with an empty string key having an empty string parameter key.
So, when call ToString on the instance returned by System.Web.HttpUtility.ParseQueryString method you would expect to get the parsed string (or, at least, one that would be parsed into the equivalent collection), right? But what you’ll get instead is this: noKey&emptyKey&A=Akey.
I’ve filed a bug into connect. If you think this is important and must be corrected, please vote.