Merge branch '3.4' into 4.3

* 3.4:
  Fix inconsistent return points.
  [Security/Core] UserInterface::getPassword() can return null
  [Router] Fix TraceableUrlMatcher behaviour with trailing slash

Author: nicolas-grekas

Command/LintCommand.php

@@ -199,10 +199,13 @@ private function getFiles($fileOrDirectory)
         }
     }
 
+    /**
+     * @return string|null
+     */
     private function getStdin()
     {
         if (0 !== ftell(STDIN)) {
-            return;
+            return null;
         }
 
         $inputs = '';

Parser.php

@@ -512,12 +512,12 @@ private function getCurrentLineIndentation(): int
      *
      * @throws ParseException When indentation problem are detected
      */
-    private function getNextEmbedBlock(int $indentation = null, bool $inSequence = false): ?string
+    private function getNextEmbedBlock(int $indentation = null, bool $inSequence = false): string
     {
         $oldLineIndentation = $this->getCurrentLineIndentation();
 
         if (!$this->moveToNextLine()) {
-            return null;
+            return '';
         }
 
         if (null === $indentation) {
@@ -560,15 +560,15 @@ private function getNextEmbedBlock(int $indentation = null, bool $inSequence = f
         } else {
             $this->moveToPreviousLine();
 
-            return null;
+            return '';
         }
 
         if ($inSequence && $oldLineIndentation === $newIndent && isset($data[0][0]) && '-' === $data[0][0]) {
             // the previous line contained a dash but no item content, this line is a sequence item with the same indentation
             // and therefore no nested list or mapping
             $this->moveToPreviousLine();
 
-            return null;
+            return '';
         }
 
         $isItUnindentedCollection = $this->isStringUnIndentedCollectionItem();