We recently upgraded our Dev and Test environment to V 9.0.
While importing a solution from Dev to Test which had SiteMap we got the below issue.
“The SiteMapName in the AppModuleSiteMap is null or empty”
It turns out that the following tags were required and were missing in the Customization.xml
We added that tag and were able to import the solution successfully.
Interestingly if we export the same solution from Test and search for this tag, it is again missing, however, we can see the following XML section added there
This section was not there in dev’s sitemap.
Hope it helps..