Trying to automate creating and deleting mongo database and user for it.
Got a problem with such code:

conn = Mongo::Connection.new("localhost")
conn.db("admin").authenticate("root", "password")
conn.db("foobar").eval("db.addUser()", "foo", "bar")

/var/lib/gems/1.8/gems/mongo-0.18.3/lib/../lib/mongo/db.rb:293:in `eval': eval failed: invoke failed: JS Error: ReferenceError: hex_md5 is not defined (anon):42 (Mongo::OperationFailure)
from ./test-mongo.rb:15

Some another evaluations from ruby script works, like:
conn.db("some_base").eval("db.dropDatabase()")

I sepose it's error from mongodb, but same evaluations in mongo shell works
use foobar;
db.addUser("foo", "bar")

Is this a bug or is there an another way to create mongodb user from ruby script?