Fixed initial Doctrine migration

forum_topics.topic_group_id could be NULL, but it shouldn't be

Signed-off-by: Gergely Polonkai (W00d5t0ck) <polesz@w00d5t0ck.info>

app/DoctrineMigrations/Version20120731113533.php

@@ -49,7 +49,7 @@ class Version20120731113533 extends AbstractMigration
         $this->addSql("CREATE TABLE forum_topic_groups (id INT AUTO_INCREMENT NOT NULL, created_by_id INT DEFAULT NULL, createdAt DATETIME NOT NULL, slug VARCHAR(100) NOT NULL, title VARCHAR(100) NOT NULL, UNIQUE INDEX UNIQ_6BB4FCEF989D9B62 (slug), UNIQUE INDEX UNIQ_6BB4FCEF2B36786B (title), INDEX IDX_6BB4FCEFB03A8386 (created_by_id), PRIMARY KEY(id)) ENGINE = InnoDB");
         $this->addSql("ALTER TABLE forum_topic_groups ADD CONSTRAINT FK_6BB4FCEFB03A8386 FOREIGN KEY (created_by_id) REFERENCES users (id)");
 
-        $this->addSql("CREATE TABLE forum_topics (id INT AUTO_INCREMENT NOT NULL, created_by_id INT DEFAULT NULL, topic_group_id INT DEFAULT NULL, last_post_id INT DEFAULT NULL, created_at DATETIME NOT NULL, slug VARCHAR(100) NOT NULL, title VARCHAR(100) NOT NULL, INDEX IDX_895975E8B03A8386 (created_by_id), INDEX IDX_895975E88655441 (topic_group_id), UNIQUE INDEX UNIQ_895975E82D053F64 (last_post_id), UNIQUE INDEX UNIQ_895975E886554412B36786B (topic_group_id, title), UNIQUE INDEX UNIQ_895975E88655441989D9B62 (topic_group_id, slug), PRIMARY KEY(id)) ENGINE = InnoDB");
+        $this->addSql("CREATE TABLE forum_topics (id INT AUTO_INCREMENT NOT NULL, created_by_id INT DEFAULT NULL, topic_group_id INT NOT NULL, last_post_id INT DEFAULT NULL, created_at DATETIME NOT NULL, slug VARCHAR(100) NOT NULL, title VARCHAR(100) NOT NULL, INDEX IDX_895975E8B03A8386 (created_by_id), INDEX IDX_895975E88655441 (topic_group_id), UNIQUE INDEX UNIQ_895975E82D053F64 (last_post_id), UNIQUE INDEX UNIQ_895975E886554412B36786B (topic_group_id, title), UNIQUE INDEX UNIQ_895975E88655441989D9B62 (topic_group_id, slug), PRIMARY KEY(id)) ENGINE = InnoDB");
         $this->addSql("ALTER TABLE forum_topics ADD CONSTRAINT FK_895975E8B03A8386 FOREIGN KEY (created_by_id) REFERENCES users (id)");
         $this->addSql("ALTER TABLE forum_topics ADD CONSTRAINT FK_895975E88655441 FOREIGN KEY (topic_group_id) REFERENCES forum_topic_groups (id)");