Merge branch '5.4' into 6.2

* 5.4:
  [Serializer] Fix CsvEncoder decode on empty data
  [Tests] Migrate data providers to static ones
  stop using assertObjectHasAttribute()/assertObjectHasNotAttribute()
  [Dotenv] Fix phpdoc Dotenv
  [Config] Fix phpdoc nullable
  Fix some typos

Tests/ParserTest.php

@@ -126,14 +126,14 @@ public function testSpecifications($expected, $yaml, $comment)
         $this->assertEquals($expected, var_export($this->parser->parse($yaml), true), $comment);
     }
 
-    public function getDataFormSpecifications()
+    public static function getDataFormSpecifications()
     {
-        return $this->loadTestsFromFixtureFiles('index.yml');
+        return self::loadTestsFromFixtureFiles('index.yml');
     }
 
-    public function getNonStringMappingKeysData()
+    public static function getNonStringMappingKeysData()
     {
-        return $this->loadTestsFromFixtureFiles('nonStringKeys.yml');
+        return self::loadTestsFromFixtureFiles('nonStringKeys.yml');
     }
 
     /**
@@ -2392,7 +2392,7 @@ public function testParsingIniThrowsException()
         $this->parser->parse($ini);
     }
 
-    private function loadTestsFromFixtureFiles($testsFile)
+    private static function loadTestsFromFixtureFiles($testsFile)
     {
         $parser = new Parser();