When an external transaction manager (e.g. on spring-boot) executes XAResource.recover() via teiid jdbc, recover can returns null. This behaviour can be seen if the teiid server haven't handle any transaction yet after starting up.

According to the javadoc, it seems that the recover() should return 0 or more length array.
"The resource manager returns zero or more XIDs of the transaction branches that are currently in a prepared or heuristically completed state."
https://docs.oracle.com/javase//8/docs/api/javax/transaction/xa/XAResource.html#recover-int-