Use valid arguments

tests/Doctrine/Tests/DBAL/Functional/Driver/SQLSrv/StatementTest.php

@@ -27,7 +27,7 @@ class StatementTest extends DbalFunctionalTestCase
     public function testFailureToPrepareResultsInException() : void
     {
         // use the driver connection directly to avoid having exception wrapped
-        $stmt = $this->connection->getWrappedConnection()->prepare(null);
+        $stmt = $this->connection->getWrappedConnection()->prepare('');
 
         // it's impossible to prepare the statement without bound variables for SQL Server,
         // so the preparation happens before the first execution when variables are already in place

tests/Doctrine/Tests/DBAL/Functional/Schema/SqliteSchemaManagerTest.php

@@ -98,7 +98,7 @@ EOS
             new Schema\ForeignKeyConstraint(
                 ['log'],
                 'log',
-                [null],
+                [''],
                 'FK_3',
                 ['onUpdate' => 'SET NULL', 'onDelete' => 'NO ACTION', 'deferrable' => false, 'deferred' => false]
             ),