Parameter "unevaluatedValue" cannot be null when saving *.rptproj project

Question

If you have existing Report Server Project in your solution and you upgrade SQL Server Data Tools from version 14.0.61707.300 to 14.0.61709.290, you can get following message when opening your existing *.rptproj files:

When you confirm upgrade by clicking on "Yes" button, solution could be successfully opened. When you try to save modified project file, you can get SaveAs... dialog and following confirmation box:

But when you confirm replacing existing project file, you could get an error from Visual Studio:

Answer 1

As I found at Community developer site, the problem is in the content of project files. To solve the situation you have to open existing *.rptproj file and manually add Platform into all build configurations, where it is missing.

After this change, Visual Studio detects that project files has been changed, so you can reload them and therefore you can save them.