document missing package error

rhel8/software.md

@@ -33,6 +33,8 @@ base::package_groups:
     - 'java'
 ```
 
+
+
 ### Install a Group of Packages
 
 To add a RedHat predefined group of packages (checkout out `dnf grouplist --hidden`) prepend the name of it with a `@`, e.g. for "Java Platform" it would be `@Java Platform`:
@@ -55,8 +57,6 @@ base::pkg_group::java:
 ```
 
 ### Install Packages only on Given OS Version
-
-**implemented only in rhel8_preprod branch**
  
  Certain packages are only used on a given OS Version, so a `os=` with the OS name and the major version selects a package only for given OS, where as a `os!` will filter away given package on hosts with given OS, so they are not installed there.
 
@@ -105,6 +105,14 @@ Then `yum_client::package_groups` is the Hiera list to contain the package group
 
 Please migrate them to the equivalent `base::*` list. You can have both of them available at the same time, with possibly the same content.
 
+### Missing Package
+
+If there is no such package in the repositories, we get the rather uninformative error message
+
+```
+Error: /Stage[main]/.../Package[nc]: Could not evaluate: no implicit conversion of Array into Hash
+```
+
 ## Managing Services with Systemd
 
 Hiera can also be used to manage services and to automate reoccuring tasks with timers.