Allow serverVersion to be explicitly unspecified (null)

lib/Doctrine/DBAL/Connection.php

@@ -418,7 +418,7 @@ private function getDatabasePlatformVersion()
         }
 
         // Explicit platform version requested (supersedes auto-detection).
-        if (isset($this->_params['serverVersion'])) {
+        if (array_key_exists('serverVersion', $this->_params)) {
             return $this->_params['serverVersion'];
         }
 

tests/Doctrine/Tests/DBAL/ConnectionTest.php

@@ -8,6 +8,7 @@
 use Doctrine\DBAL\Events;
 use Doctrine\Tests\Mocks\DriverConnectionMock;
 use Doctrine\Tests\Mocks\DriverMock;
+use Doctrine\Tests\Mocks\VersionAwareDriverMock;
 
 class ConnectionTest extends \Doctrine\Tests\DbalTestCase
 {
@@ -563,4 +564,23 @@ public function testPlatformDetectionIsTriggerOnlyOnceOnRetrievingPlatform()
 
         $this->assertSame($platformMock, $connection->getDatabasePlatform());
     }
+
+    public function testNullServerVersionDoesNotTriggerDatabaseConnect()
+    {
+        $driverMock = new VersionAwareDriverMock();
+        $params = $this->params;
+        $params['serverVersion'] = null;
+
+        $connection = $this->getMock(
+            'Doctrine\DBAL\Connection',
+            array('connect'),
+            array($params, $driverMock)
+        );
+
+        $connection->expects($this->never())
+            ->method('connect');
+
+
+        $connection->getDatabasePlatform();
+    }
 }

tests/Doctrine/Tests/Mocks/VersionAwareDriverMock.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace Doctrine\Tests\Mocks;
+
+use Doctrine\DBAL\DBALException;
+use Doctrine\DBAL\VersionAwarePlatformDriver;
+
+class VersionAwareDriverMock extends DriverMock implements VersionAwarePlatformDriver
+{
+    /**
+     * Factory method for creating the appropriate platform instance for the given version.
+     *
+     * @param string $version The platform/server version string to evaluate. This should be given in the notation
+     *                        the underlying database vendor uses.
+     *
+     * @return \Doctrine\DBAL\Platforms\AbstractPlatform
+     *
+     * @throws DBALException if the given version string could not be evaluated.
+     */
+    public function createDatabasePlatformForVersion($version)
+    {
+        throw new DBALException('PHPUnit');
+    }
+}