Convert solution format dialog is not displayed

[mrward]

VS Mac 7.6 and 7.7.

Looks like this was broken in VS Mac 7.5.4 - #4597

Selecting Tools - Convert Solution Format, either with from the solution or project, does not open the Convert solution format dialog.

IDE log has a null reference exception (VS Mac 7.6.8).

An unhandled exception has occurred. Terminating Visual Studio? False
System.NullReferenceException: Object reference not set to an instance of an object
  at MonoDevelop.Ide.Projects.ExportSolutionDialog..ctor (MonoDevelop.Projects.IMSBuildFileObject item, MonoDevelop.Projects.MSBuild.MSBuildFileFormat selectedFormat) [0x0000c] in /Users/vsts/agent/2.140.2/work/1/s/monodevelop/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.Projects/ExportSolutionDialog.cs:46 
  at MonoDevelop.Ide.ProjectOperations+<Export>d__45.MoveNext () [0x0000a] in /Users/vsts/agent/2.140.2/work/1/s/monodevelop/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide/ProjectOperations.cs:390 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.CompilerServices.AsyncMethodBuilderCore+<>c.<ThrowAsync>b__6_0 (System.Object state) [0x00000] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-04/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/AsyncMethodBuilder.cs:1018 
  at MonoDevelop.Ide.DispatchService+GtkSynchronizationContext+TimeoutProxy.HandlerInternal (System.IntPtr data) [0x00014] in /Users/vsts/agent/2.140.2/work/1/s/monodevelop/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide/DispatchService.cs:77 

VS bug #698903