show apt-cache output if packageversion empty during specified repo

api

@@ -600,6 +600,9 @@ install_packages() { #Make some packages dependencies of the $app app. Package-n
     #request package version if backports repo was specified
     elif [ ! -z "$repo_selection" ];then
       local packageversion="$(package_latest_version "$package" -t "$repo_selection" | sed 's/+.*//g')"
+      if [ -z "$packageversion" ];then
+        error "install_packages(): failed to get package version for $package, apt-cache output was $(apt-cache policy -t "$repo_selection" "$package" 2>&1)"
+      fi
       #add version specification to package
       packages="$(echo "$packages" | sed "s|^${package}$|$package (>= $packageversion)|")"
     fi