Merge branch '5.2' into 5.x

* 5.2:
  [Finder] Fix gitignore regex build with "**"
  Fixed deprecation warnings about passing null as parameter
  [Security] Keep Bulgarian wording consistent across all texts.
  Migrate configuration file for PHP CS Fixer 2.19/3.0
  [Form] Replace broken ServerParams mock
  [Mailer] Fix SES API call with UTF-8 Addresses

Author: fabpot

Generator/UrlGenerator.php

@@ -189,7 +189,7 @@ protected function doGenerate(array $variables, array $defaults, array $requirem
 
                 if (!$optional || $important || !\array_key_exists($varName, $defaults) || (null !== $mergedParams[$varName] && (string) $mergedParams[$varName] !== (string) $defaults[$varName])) {
                     // check requirement (while ignoring look-around patterns)
-                    if (null !== $this->strictRequirements && !preg_match('#^'.preg_replace('/\(\?(?:=|<=|!|<!)((?:[^()\\\\]+|\\\\.|\((?1)\))*)\)/', '', $token[2]).'$#i'.(empty($token[4]) ? '' : 'u'), $mergedParams[$token[3]])) {
+                    if (null !== $this->strictRequirements && !preg_match('#^'.preg_replace('/\(\?(?:=|<=|!|<!)((?:[^()\\\\]+|\\\\.|\((?1)\))*)\)/', '', $token[2]).'$#i'.(empty($token[4]) ? '' : 'u'), $mergedParams[$token[3]] ?? '')) {
                         if ($this->strictRequirements) {
                             throw new InvalidParameterException(strtr($message, ['{parameter}' => $varName, '{route}' => $name, '{expected}' => $token[2], '{given}' => $mergedParams[$varName]]));
                         }