Bug 58018 - Concatenating null strings leads to incorrect results
Summary: Concatenating null strings leads to incorrect results
Alias: None
Product: Workbooks & Inspector
Classification: Xamarin
Component: Actually Unsure ()
Version: master
Hardware: PC Mac OS
: --- normal
Target Milestone: ---
Assignee: xamarininteractive
Depends on:
Reported: 2017-07-07 21:13 UTC by Larry O'Brien
Modified: 2017-08-21 17:28 UTC (History)
2 users (show)

Is this bug a regression?: ---
Last known good build:

Workbook demonstrating behavior (707 bytes, text/plain)
2017-07-07 21:13 UTC, Larry O'Brien

Notice (2018-05-24): bugzilla.xamarin.com is now in read-only mode.

Please join us on Visual Studio Developer Community and in the Xamarin and Mono organizations on GitHub to continue tracking issues. Bugzilla will remain available for reference in read-only mode. We will continue to work on open Bugzilla bugs, copy them to the new locations as needed for follow-up, and add the new items under Related Links.

Our sincere thanks to everyone who has contributed on this bug tracker over the years. Thanks also for your understanding as we make these adjustments and improvements for the future.

Please create a new report on Developer Community with your current version information, steps to reproduce, and relevant error messages or log files if you are hitting an issue that looks similar to this resolved bug and you do not yet see a matching new report.

Related Links:

Description Larry O'Brien 2017-07-07 21:13:55 UTC
Created attachment 23413 [details]
Workbook demonstrating behavior

Evaluating `((string) null) + ( (string) null)` in Workbooks shows an evaluation of `null`, but it should evaluate to an empty string (""). Also:

var s = (string)null;
"" + s;

evaluates to `null` but should evaluate to `""`. 

FWIW, "A" + s evaluates properly to "A" 

According to "https://github.com/dotnet/csharplang/blob/master/spec/expressions.md#arithmetic-operators" 

"These overloads of the binary + operator perform string concatenation. If an operand of string concatenation is null, an empty string is substituted. Otherwise, any non-string argument is converted to its string representation by invoking the virtual ToString method inherited from type object. If ToString returns null, an empty string is substituted."