[Serializer] Remove null check

src/Symfony/Component/Serializer/Encoder/CsvEncoder.php

@@ -196,24 +196,18 @@ private function flatten(array $array, array &$result, $keySeparator, $parentKey
 
     /**
      * Ensures an actual value is used instead of a blank value when dealing
-     * with true, false and null (like a nullable bool in a database).
+     * with true and false.
      *
      * @param string $value
      *
-     * @return string|int
+     * @return int
      */
     private function cleanValueByType($value)
     {
         if (false === $value) {
             return 0;
         }
 
-        if (null === $value) {
-            // fputcsv will enclose a space
-            // https://github.com/php/php-src/blob/master/ext/standard/file.c
-            return ' ';
-        }
-
         if (true === $value) {
             return 1;
         }