Use main window as current UI if not already set #9443

1 files changed, 5 insertions, 0 deletions

diff --git a/server/src/com/vaadin/Application.java b/server/src/com/vaadin/Application.java
index e4e49391bb..9498534b4a 100644
--- a/server/src/com/vaadin/Application.java
+++ b/server/src/com/vaadin/Application.java
@@ -185,6 +185,11 @@ public class Application implements Terminal.ErrorListener, Serializable {
                 throw new IllegalStateException(
                         "mainWindow is attached to another application");
             }
+            if (UI.getCurrent() == null) {
+                // Assume setting a main window from Application.init if there's
+                // no current UI -> set the main window as the current UI
+                UI.setCurrent(mainWindow);
+            }
             this.mainWindow = mainWindow;
         }