When there is a FieldException on a Logon message (e.g. mandatory field not set or field specified without a value) it is tried to reject the message with a session-level reject.
This of course fails because no session is established yet:

quickfix.SessionException: Tried to send a reject while not logged on

Moreover, the session is not disconnected.

This should be changed so that a Logout message with a descriptive error text is sent back to the counterparty and the session should be disconnected directly afterwards.