Fix an NPE caused by the previous fix to Grid's frozen columns (#11444)

* Fix an NPE caused by the previous fix to Grid's frozen columns (#10653)

If the user managed to get two frozen column count changes into a single server round-trip before the component had been attached, the previous fix  #11346 lead to a null pointer exception since there was no diff state available.

This fix adds a null check before removing the frozen column count value from the diff state so that this will not happen.

Closes #10653

1 files changed, 6 insertions, 2 deletions

diff --git a/server/src/main/java/com/vaadin/ui/Grid.java b/server/src/main/java/com/vaadin/ui/Grid.java
index 7c3467eaa3..3d687136cd 100644
--- a/server/src/main/java/com/vaadin/ui/Grid.java
+++ b/server/src/main/java/com/vaadin/ui/Grid.java
@@ -3093,8 +3093,12 @@ public class Grid<T> extends AbstractListing<T> implements HasComponents,
             final String diffStateKey = "frozenColumnCount";
             UI ui = getUI();
             if (ui != null) {
-                ui.getConnectorTracker().getDiffState(Grid.this)
-                        .remove(diffStateKey);
+                JsonObject diffState = ui.getConnectorTracker()
+                        .getDiffState(Grid.this);
+                // if diffState is not present, there's nothing for us to clean
+                if (diffState != null) {
+                    diffState.remove(diffStateKey);
+                }
             }
         }
         getState().frozenColumnCount = numberOfColumns;