Merge pull request #5172 from nextcloud/preventNPE

prevent NPE

src/main/java/com/owncloud/android/ui/fragment/OCFileListFragment.java

@@ -792,8 +792,11 @@ public class OCFileListFragment extends ExtendedListFragment implements
         }
 
         // create rich workspace
-        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
-            menu.findItem(R.id.action_create_rich_workspace).setVisible(TextUtils.isEmpty(mFile.getRichWorkspace()));
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP
+            && menu.findItem(R.id.action_create_rich_workspace) != null
+            && mFile != null) {
+            menu.findItem(R.id.action_create_rich_workspace).setVisible(
+                TextUtils.isEmpty(mFile.getRichWorkspace()));
         }
     }