Add missing null check to Binding (#10726)

* Add missing null check to Binding

server/src/main/java/com/vaadin/data/Binder.java

@@ -1139,9 +1139,11 @@ public class Binder<BEAN> implements Serializable {
          */
         private void handleFieldValueChange(
                 ValueChangeEvent<FIELDVALUE> event) {
-            // Inform binder of changes; if setBean: writeIfValid
-            getBinder().handleFieldValueChange(this, event);
-            getBinder().fireValueChangeEvent(event);
+            if (binder != null) {
+                // Inform binder of changes; if setBean: writeIfValid
+                getBinder().handleFieldValueChange(this, event);
+                getBinder().fireValueChangeEvent(event);
+            }
         }
 
         /**

server/src/test/java/com/vaadin/data/BinderTest.java

@@ -811,6 +811,25 @@ public class BinderTest extends BinderTestBase<Binder<Person>, Person> {
                 String.valueOf(item.getAge()), ageField.getValue());
     }
 
+    @Test
+    public void remove_binding_fromFieldValueChangeListener() {
+        // Add listener before bind to make sure it will be executed first.
+        nameField.addValueChangeListener(e -> {
+            if (e.getValue() == "REMOVE") {
+                binder.removeBinding(nameField);
+            }
+        });
+
+        binder.bind(nameField, Person::getFirstName, Person::setFirstName);
+
+        binder.setBean(item);
+
+        nameField.setValue("REMOVE");
+
+        // Removed binding should not update bean.
+        assertNotEquals("REMOVE", item.getFirstName());
+    }
+
     @Test
     public void beanvalidation_two_fields_not_equal() {
         TextField lastNameField = new TextField();