Dashboard: Display error message on failure

When no (default) configuration is available for dashboards
application dies not very gracefully. Display error message
and guid the user to the solution is a better way.

fixes #6412

application/controllers/DashboardController.php

@@ -46,6 +46,11 @@ use Icinga\Web\Controller\ActionController;
  */
 class DashboardController extends ActionController
 {
+    /**
+     * Default configuration
+     */
+    const DEFAULT_CONFIG = 'dashboard/dashboard';
+
     /**
      * Retrieve a dashboard from the provided config
      *
@@ -53,14 +58,18 @@ class DashboardController extends ActionController
      *
      * @return  \Icinga\Web\Widget\Dashboard
      */
-    private function getDashboard($config = 'dashboard/dashboard')
+    private function getDashboard($config = self::DEFAULT_CONFIG)
     {
         $dashboard = new Dashboard();
         try {
             $dashboardConfig = IcingaConfig::app($config);
+            if (count($dashboardConfig) === 0) {
+                return null;
+            }
             $dashboard->readConfig($dashboardConfig);
         } catch (NotReadableError $e) {
             Logger::error(new Exception('Cannot load dashboard configuration. An exception was thrown:', 0, $e));
+            return null;
         }
         return $dashboard;
     }
@@ -133,8 +142,15 @@ class DashboardController extends ActionController
             $pane = $this->_getParam('pane');
             $dashboard->activate($pane);
         }
+
+        $this->view->configPath = IcingaConfig::$configDir . DIRECTORY_SEPARATOR . self::DEFAULT_CONFIG;
+
+        if ($dashboard === null) {
+            $this->view->title = 'Dashboard';
+        } else {
             $this->view->title = $dashboard->getActivePane()->getTitle() . ' :: Dashboard';
             $this->view->tabs = $dashboard->getTabs();
+
                 /* Temporarily removed
                 $this->view->tabs->add(
                     'Add',
@@ -144,7 +160,10 @@ class DashboardController extends ActionController
                     )
                 );
                 */
+
             $this->view->dashboard = $dashboard;
+
+        }
     }
 
     /**

application/views/scripts/dashboard/index.phtml

@@ -1,6 +1,20 @@
 <div class="controls">
 <?= $this->tabs ?>
 </div>
+<?php if ($this->dashboard): ?>
     <div class="dashboard content">
     <?= $this->dashboard ?>
     </div>
+<?php else: ?>
+    <div class="content">
+        <h1>No dashboard configuration found!</h1>
+        <p>
+            We tried to load a dashboard configuration with no success.
+            Please have look that the configuration does exist:
+
+            <code>
+                <?= $this->configPath ?>.ini
+            </code>
+        </p>
+    </div>
+<?php endif; ?>

library/Icinga/Web/Widget/Dashboard.php

@@ -305,7 +305,7 @@ class Dashboard extends AbstractWidget
                 $active = $this->setDefaultPane();
             }
         }
-        return $this->panes[$active];
+        return isset($this->panes[$active]) ? $this->panes[$active] : null;
     }
 
     /**