MongoTransactionManager.debugString() always contains error

[kacz]

If server session is not null, String formatting in MongoTransactionManager.debugString() fails and therefore the output always contains "error = d != java.lang.Boolean".
The root cause is on line String.format("closed = %d, ", session.getServerSession().isClosed()) as boolean is not accepted by %d.

[christophstrobl]

Good catch @kacz! Should have been %b.