feature(popup): staticBackdrop/modal

* fix NPE

Issue: TOBAGO-2298
diff --git a/tobago-core/src/main/java/org/apache/myfaces/tobago/internal/component/AbstractUIPopup.java b/tobago-core/src/main/java/org/apache/myfaces/tobago/internal/component/AbstractUIPopup.java
index 56d74c1..3320ff1 100644
--- a/tobago-core/src/main/java/org/apache/myfaces/tobago/internal/component/AbstractUIPopup.java
+++ b/tobago-core/src/main/java/org/apache/myfaces/tobago/internal/component/AbstractUIPopup.java
@@ -30,7 +30,7 @@
   @Override
   public void processUpdates(final FacesContext facesContext) {
     super.processUpdates(facesContext);
-    if (getSubmittedCollapsed()) {
+    if (getSubmittedCollapsed() != null && getSubmittedCollapsed()) {
       // process state when the popup is closed by clicking on the background or pressing ESC.
       processState();
     }