There is nothing on left. It is a maven project. Why?

There is nothing on left. It is a maven project. Why?

I've had the same problem and narrowed it down to the following configuration that might have been messed up during the upgrade.
File (on Mac): ~/Library/Preferences/IntelliJIdea2018.1/options/projectView.xml
<application>
<component name="ProjectViewSharedSettings">
<option name="showLibraryContents" value="false" />
<option name="showMembers" value="true" />
</component>
</application>
Change/remove the showLibraryContents entry. This setting is no longer available in the UI, "External Libraries" are always shown.
I solved this by selecting "Project" as view (by default i had "Project Files"). Hope this helped.
I was facing the same issue on windows, i solved it by
right click on pom.xml > maven > reimport
Then reopen the project, It worked for me.
If maven re-import does nothing, check your pom.xml for errors and try commenting out the offending ones (marked in red).
In Intellij: Ctrl + Alt + Shift + S -> Select Modules and ensure that there is only one module. Delete the other ones.
If all else fails: In Intellij, Select "Invalidate caches/Restart" -> Close Intellij -> Go to the project folder and delete .idea folder -> Reopen Intellij and "mvn clean install"