Add open solution check

Author: Maria Solano

src/toolkit/Community.VisualStudio.Toolkit.Shared/Solution/Solutions.cs

@@ -3,6 +3,7 @@
 using System.Linq;
 using System.Runtime.InteropServices;
 using System.Threading.Tasks;
+using Microsoft.Internal.VisualStudio.PlatformUI;
 using Microsoft.VisualStudio;
 using Microsoft.VisualStudio.Shell;
 using Microsoft.VisualStudio.Shell.Interop;
@@ -24,6 +25,12 @@ internal Solutions()
         public async Task<Solution?> GetCurrentSolutionAsync()
         {
             await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync();
+
+            if (!HierarchyUtilities.IsSolutionOpen)
+            {
+                return null;
+            }
+
             IVsHierarchy solution = (IVsHierarchy)await VS.Services.GetSolutionAsync();
             IVsHierarchyItem hierItem = await solution.ToHierarchyItemAsync(VSConstants.VSITEMID_ROOT);
             return SolutionItem.FromHierarchyItem(hierItem) as Solution;