Move assigned_valuators from helper to model

There's no good reason to call assigned_valuators(investment) when the
logic can be at the model.

Also removed the valuator_groups texts to be added in an independent
method

app/helpers/valuation_helper.rb

@@ -13,11 +13,6 @@ module ValuationHelper
     ValuatorGroup.order("name ASC").collect { |g| [ g.name, "group_#{g.id}"] }
   end
 
-  def assigned_valuators(investment)
-    [investment.valuator_groups.collect(&:name) +
-     investment.valuators.collect(&:description_or_name)].flatten.join(', ')
-  end
-
   def assigned_valuators_info(valuators)
     case valuators.size
     when 0

app/models/budget/investment.rb

@@ -320,6 +320,14 @@ class Budget
       investments
     end
 
+    def assigned_valuators
+      self.valuators.collect(&:description_or_name).compact.join(', ').presence
+    end
+
+    def assigned_valuation_groups
+      self.valuator_groups.collect(&:name).compact.join(', ').presence
+    end
+
     def self.to_csv(investments, options = {})
       attrs = [I18n.t("admin.budget_investments.index.table_id"),
                I18n.t("admin.budget_investments.index.table_title"),

app/views/admin/budget_investments/_investments.html.erb

@@ -63,7 +63,7 @@
             <% if investment.valuators.size == 0 && investment.valuator_groups.size == 0  %>
               <%= t("admin.budget_investments.index.no_valuators_assigned") %>
             <% else %>
-              <%= assigned_valuators(investment) %>
+              <%= investment.assigned_valuators %>
             <% end %>
           </td>
           <td class="small">