REPL instructions in migrations.html not working

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To interactively create a new migration, https://luminusweb.com/docs/migrations.html tells you to do this:

```
(mount.core/start #'.db.core/*db*)
(user/create-migration "add-users-table")
```

I can not get this to work. Fresh sample project created this week via `lein new luminus foobar +postgres`, then adjusting `:database-url` in `dev-config.edn`, the db connection is known to work via `lein run`.

This is what I get:
```
$ cd foobar
$ lein repl

user=> (mount.core/start #'foobar.db.core/*db*)
Execution error (ClassCastException) at foobar.db.core/eval13540$fn (core.clj:14).
class mount.core.DerefableState cannot be cast to class clojure.lang.IFn (mount.core.DerefableState is in unnamed module of loader clojure.lang.DynamicClassLoader @57540fd0; clojure.lang.IFn is in unnamed module of loader 'app')

### this is the error that confuses me

user=> (user/start)
2021-12-30 09:48:46,579 [nREPL-session-b1f4b012-2cd9-4cfa-87a4-e9f735c8e430] ERROR luminus.http-server - server failed to start on port: 3000
java.lang.RuntimeException: java.net.BindException: Address already in use

# this is not the problem, I know it's running, but I was playing around a bit

user=> (user/create-migration "foo" )
nil

### nothing happened

user=> (mount.core/start #'foobar.db.core/*db*)
{:started []}

### no more error

user=> (user/create-migration "change-something" )
nil

### still nothing happened
```

Also the line before the `mount.start` reads:

```
(defstate ^:dynamic *db*
:start (conman/connect! {:jdbc-url (env :database-url)})
:stop (conman/disconnect! *db*))
```

whereas in the code it is currently

```
(defstate ^:dynamic *db*
:start (if-let [jdbc-url (env :database-url)]
(conman/connect! {:jdbc-url jdbc-url})
(do
(log/warn "database connection URL was not found, please set :database-url in your config, e.g: dev-config.edn")
*db*))
:stop (conman/disconnect! *db*))
```

and I can't tell if that's a simplified version by default, or if it has changed meanwhile, or something else

Read migrations.html alongside the generated foobar.db.core code and reproduce the documented REPL commands in the sample project described. Check whether the instructions match the current template and verify that the corrected workflow creates a migration file without the reported errors.

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