Merge branch '3.0'

* 3.0:
  [Form] [ChoiceType] Prefer placeholder to empty_value
  Add missing RFC comment
  ensure dump indentation to be greather than zero

src/Symfony/Component/Form/Tests/Extension/Core/Type/ChoiceTypeTest.php

@@ -1435,7 +1435,7 @@ class ChoiceTypeTest extends \Symfony\Component\Form\Test\TypeTestCase
         ));
         $view = $form->createView();
 
-        $this->assertEquals($viewValue, $view->vars['placeholder']);
+        $this->assertSame($viewValue, $view->vars['placeholder']);
         $this->assertFalse($view->vars['placeholder_in_choices']);
     }
 

src/Symfony/Component/HttpFoundation/Response.php

@@ -170,7 +170,7 @@ class Response
         428 => 'Precondition Required',                                       // RFC6585
         429 => 'Too Many Requests',                                           // RFC6585
         431 => 'Request Header Fields Too Large',                             // RFC6585
-        451 => 'Unavailable For Legal Reasons',
+        451 => 'Unavailable For Legal Reasons',                               // RFC7725
         500 => 'Internal Server Error',
         501 => 'Not Implemented',
         502 => 'Bad Gateway',

src/Symfony/Component/Yaml/Dumper.php

@@ -30,6 +30,10 @@ class Dumper
      */
     public function __construct($indentation = 4)
     {
+        if ($indentation < 1) {
+            throw new \InvalidArgumentException('The indentation must be greater than zero.');
+        }
+
         $this->indentation = $indentation;
     }
 

src/Symfony/Component/Yaml/Tests/DumperTest.php

@@ -347,6 +347,24 @@ EOF;
 
         $this->assertSame(file_get_contents(__DIR__.'/Fixtures/multiple_lines_as_literal_block.yml'), $this->dumper->dump($data, 3, 0, Yaml::DUMP_MULTI_LINE_LITERAL_BLOCK));
     }
+
+    /**
+     * @expectedException \InvalidArgumentException
+     * @expectedExceptionMessage The indentation must be greater than zero
+     */
+    public function testZeroIndentationThrowsException()
+    {
+        new Dumper(0);
+    }
+
+    /**
+     * @expectedException \InvalidArgumentException
+     * @expectedExceptionMessage The indentation must be greater than zero
+     */
+    public function testNegativeIndentationThrowsException()
+    {
+        new Dumper(-4);
+    }
 }
 
 class A

src/Symfony/Component/Yaml/Tests/YamlTest.php

@@ -22,4 +22,22 @@ class YamlTest extends \PHPUnit_Framework_TestCase
         $parsed = Yaml::parse($yml);
         $this->assertEquals($data, $parsed);
     }
+
+    /**
+     * @expectedException \InvalidArgumentException
+     * @expectedExceptionMessage The indentation must be greater than zero
+     */
+    public function testZeroIndentationThrowsException()
+    {
+        Yaml::dump(array('lorem' => 'ipsum', 'dolor' => 'sit'), 2, 0);
+    }
+
+    /**
+     * @expectedException \InvalidArgumentException
+     * @expectedExceptionMessage The indentation must be greater than zero
+     */
+    public function testNegativeIndentationThrowsException()
+    {
+        Yaml::dump(array('lorem' => 'ipsum', 'dolor' => 'sit'), 2, -4);
+    }
 }