Unable to use connection pooling
```
import norm/[model, sqlite, pool]
import user


proc myDb(): DbConn = open("mydb.db", "", "", "")


var connPool* = newPool[DbConn](10,myDb)

proc initDb*() =
  withDb(connPool):
    db.createTables(newUser())

proc resetPool*() =
  connPool.reset()

proc closePool*() =
  close(connPool)
```
error message

`C:\Users\.nimble\pkgs2\norm-2.8.3-c79c7ce80ebc2264679d6a252b0250ed3b4bd867\norm\pool.nim(20, 70) Error: type mismatch: got 'None' for 'getDb' but expected 'proc (): T: DbConn{.closure.}'`