A change to one of the tests exposed that we dereference pointers in the session and connection handle without checking for validity.

It's tempting to either add a NULL check or a WT_ASSERT checking for a NULL session to the include/api.h API_CALL macros.

Adding the check didn't solve the particular test issue. The test (test_txn01) was doing:

self.session.begin_transaction()
cursor = self.session.open_cursor(self.uri, None)
cursor.reset()
session.commit_transaction()
cursor.reset()

The commit_transaction call frees the cursor structure (via __wt_cursor_close). The second cursor.reset call is operating on a freed pointer - thus the cursor.session field can't be accessed safely.