handleShowColumn crash when all columns are shown (#1152)

array_search(): Argument #2 ($haystack) must be of type array, null given

src/Datagrid.php

@@ -2046,7 +2046,7 @@ public function handleShowColumn(string $column): void
 	{
 		$columns = $this->getSessionData('_grid_hidden_columns');
 
-		if ($columns !== []) {
+		if ($columns !== [] && $columns !== null) {
 			$pos = array_search($column, $columns, true);
 
 			if ($pos !== false) {