Generate SQL file without reference schema

there is a possibility for Liquibase to generate sql file using updateSql. Also now offline mode is available but you need to provide changelog as a changelog table. But why it is not possible to generate an SQL file without any schema just having if clause to apply or skip migrations, for example:

if <databasechangelog not contains migration_1>

then

    migration_1

    mark migration_1 as completed

end

...

      

So in this case we can generate SQL file without having any reference schemas. What do you think about this idea or, probably, it is already implemented?

Thanks!