Merge branch 'develop' of https://github.com/getgrav/grav into 1.6

# Conflicts:
#	CHANGELOG.md

CHANGELOG.md

@@ -58,6 +58,12 @@
     * Doctrine filecache is now namespaced with prefix to support purging
     * Register all page types into `blueprint://pages` stream
     
+# v1.5.4
+## mm/dd/2018
+
+1. [](#bugfix)
+    * Fixed fatal error if calling `$session->invalidate()` when there's no active session
+    
 # v1.5.3
 ## 10/08/2018
 

system/src/Grav/Framework/Session/Session.php

@@ -225,8 +225,10 @@ class Session implements SessionInterface
             $params['httponly']
         );
 
-        session_unset();
-        session_destroy();
+        if ($this->isSessionStarted()) {
+            session_unset();
+            session_destroy();
+        }
 
         $this->started = false;