Fix: missing roots display (#348)

* remove dead code

* return the first concept if there is no roots

* return AlertMessageComponent if skos and empty roots

* Fix message text

app/controllers/application_controller.rb

@@ -466,8 +466,8 @@ def get_class(params)
         root_child = @root.children.first
 
         @concept = root_child.explore.self(full: true)
-        # Some ontologies have "too many children" at their root. These will not process and are handled here.
-        if @concept.nil?
+         # Some ontologies have "too many children" at their root. These will not process and are handled here.
+         if @concept.nil?
           LOG.add :debug, "Missing class #{root_child.links.self}"
           not_found("Missing class #{root_child.links.self}")
         end

app/views/ontologies/concepts_browsers/_concepts_tree.html.haml

@@ -19,7 +19,7 @@
     - if skos? && @roots.empty?
       %div.text-wrap
         = render AlertMessageComponent.new do
-          Missing roots for #{@ontology.acronym}
+          Missing roots for #{@ontology.acronym} (skos:topConceptOf)
     - else
       = render TurboFrameComponent.new(id: 'concepts_tree_view',
                                      src: "/ajax/classes/treeview?ontology=#{@ontology.acronym}&conceptid=#{escape(@concept.id)}&concept_schemes=#{params[:concept_schemes]}&auto_click=false",