fix: reset grid column width when setWidth(null) is called

vaadin-grid-flow-parent/vaadin-grid-flow/src/main/java/com/vaadin/flow/component/grid/Grid.java

@@ -625,12 +625,16 @@
          * @see #setFlexGrow(int)
          *
          * @param width
-         *            the width to set this column to, as a CSS-string, not
-         *            {@code null}
+         *            the width to set this column to, as a CSS-string, or
+         *            {@code null} to reset the width to the default
          * @return this column, for method chaining
          */
         public Column<T> setWidth(String width) {
-            getElement().setProperty("width", width);
+            if (width != null) {
+                getElement().setProperty("width", width);
+            } else {
+                getElement().removeProperty("width");
+            }
             return this;
         }
 

vaadin-grid-flow-parent/vaadin-grid-flow/src/test/java/com/vaadin/flow/component/grid/GridColumnTest.java

@@ -149,6 +149,21 @@ void removeColumnTwice_throws() {
                 "The column with key 'first' is not owned by this Grid"));
     }
 
+    @Test
+    void setWidth_getWidth() {
+        firstColumn.setWidth("100px");
+        Assertions.assertEquals("100px", firstColumn.getWidth());
+        Assertions.assertTrue(firstColumn.getElement().hasProperty("width"));
+    }
+
+    @Test
+    void setWidthNull_widthPropertyRemoved() {
+        firstColumn.setWidth("100px");
+        firstColumn.setWidth(null);
+        Assertions.assertNull(firstColumn.getWidth());
+        Assertions.assertFalse(firstColumn.getElement().hasProperty("width"));
+    }
+
     @Test
     void addColumn_defaultComparator() {
         Grid<Person> grid = new Grid<>();