Register style can be skipped when already registered

src/Spout/Writer/Common/Manager/Style/StyleManagerInterface.php

@@ -24,7 +24,7 @@ interface StyleManagerInterface
      * Typically, set "wrap text" if a cell contains a new line.
      *
      * @param Cell $cell
-     * @return Style The updated style
+     * @return Style|null The eventually updated style
      */
-    public function applyExtraStylesIfNeeded(Cell $cell);
+    public function applyExtraStylesIfNeeded(Cell $cell) : ?Style;
 }