Make it possible to override useNullAsDefault

refs #6623, #6637

- this was supposed to be in the original

core/server/data/db/connection.js

@@ -23,7 +23,7 @@ function configure(dbConfig) {
     }
 
     if (client === 'sqlite3') {
-        dbConfig.useNullAsDefault = false;
+        dbConfig.useNullAsDefault = dbConfig.useNullAsDefault || false;
     }
 
     return dbConfig;