QueryString.Create(...) excludes key when StringValues is empty

[aspnet-hello]

From @austindrenski on Thursday, November 16, 2017 3:49:22 PM

QueryString.Create(IEnumerable<KeyValuePair<string, StringValues>> parameters) doesn't append a key unless it has associated values.

This was unexpected because it means that parsing an incoming query string into an IEnumerable<KeyValuePair<string, StringValues>> and then immediately reconstructing a QueryString results in information loss.

We ran across this after some new middleware attempted to validate parameter values (by treating all query string entries as KeyValuePair<string, StringValues>) and unexpectedly removed a key meant to be read as a switch/flag/indicator in the event no values are supplied.

Is this behavior intentional or defined by a standard?

https://github.com/aspnet/HttpAbstractions/blob/476333771cb7399af13c1368982e2b8abb4318ac/src/Microsoft.AspNetCore.Http.Abstractions/QueryString.cs#L153-L175

Copied from original issue: aspnet/HttpAbstractions#969

[aspnet-hello]

From @jkotalik on Thursday, November 16, 2017 4:19:44 PM

By the RFC 3986, QueryStrings don't need to have key=value data. So it does seem like a bug, however it is odd that you are using a special flag in the query string. Maybe as a work around, you can just check if the QueryString is empty rather than relying on a special value?