diff --git a/ln.build/pipeline/DotNetCommands.cs b/ln.build/pipeline/DotNetCommands.cs
index 5970959..dbd19e0 100644
--- a/ln.build/pipeline/DotNetCommands.cs
+++ b/ln.build/pipeline/DotNetCommands.cs
@@ -40,7 +40,6 @@ namespace ln.build.commands
 
             foreach (string projectFileName in projectFiles)
             {
-                stage.PipeLine.CommandEnvironment.Extend("DOTNET_PROJECTS", projectFileName);
                 CSProjHelper csp = new CSProjHelper(projectFileName);
 
                 string projectName = csp.GetName();
@@ -49,8 +48,13 @@ namespace ln.build.commands
 
                 stage.CommandEnvironment.Logger.Log(LogLevel.INFO, "dotnet prepare: project {0} version={1} type={2}", projectName, projectVersion, ot);
 
+                if (projectVersion == null)
+                    continue;
+
                 if (projectVersion > highestVersion)
                     highestVersion = projectVersion;
+                
+                stage.PipeLine.CommandEnvironment.Extend("DOTNET_PROJECTS", projectFileName);
             }
 
             stage.PipeLine.CommandEnvironment.Set("RELEASE_VERSION", highestVersion.ToString());