minor #59898 replace assertEmpty() with stricter assertions (xabbuh)

This PR was merged into the 7.3 branch.

Discussion
----------

replace `assertEmpty()` with stricter assertions

| Q             | A
| ------------- | ---
| Branch?       | 7.3
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        |
| License       | MIT

In the code we are strict about not using `empty()`. In my opinion it makes sense to be equally strict with our assertions. But I'd like to gather some feedback first before updating all places.

Commits
-------

6550cb815e3 replace assertEmpty() with stricter assertions

Author: fabpot

Tests/ParameterBagTest.php

@@ -253,7 +253,7 @@ public function testFilter()
             'array' => ['bang'],
         ]);
 
-        $this->assertEmpty($bag->filter('nokey'), '->filter() should return empty by default if no key is found');
+        $this->assertSame('', $bag->filter('nokey'), '->filter() should return empty by default if no key is found');
 
         $this->assertEquals('0123', $bag->filter('digits', '', \FILTER_SANITIZE_NUMBER_INT), '->filter() gets a value of parameter as integer filtering out invalid characters');
 

Tests/ResponseTest.php

@@ -127,7 +127,7 @@ public function testSetNotModified()
         ob_start();
         $modified->sendContent();
         $string = ob_get_clean();
-        $this->assertEmpty($string);
+        $this->assertSame('', $string);
     }
 
     public function testIsSuccessful()

Tests/Session/Storage/Handler/PdoSessionHandlerTest.php

@@ -352,7 +352,7 @@ public function testConfigureSchemaTableExistsPdo()
         $pdoSessionHandler = new PdoSessionHandler($this->getMemorySqlitePdo());
         $pdoSessionHandler->configureSchema($schema, fn () => true);
         $table = $schema->getTable('sessions');
-        $this->assertEmpty($table->getColumns(), 'The table was not overwritten');
+        $this->assertSame([], $table->getColumns(), 'The table was not overwritten');
     }
 
     public static function provideUrlDsnPairs()

Tests/StreamedResponseTest.php

@@ -133,7 +133,7 @@ public function testSetNotModified()
         ob_start();
         $modified->sendContent();
         $string = ob_get_clean();
-        $this->assertEmpty($string);
+        $this->assertSame('', $string);
     }
 
     public function testSendInformationalResponse()