v1 was here:
https://www.redhat.com/archives/libguestfs/2020-February/msg00081.html
v2 replaces
struct connection *conn = GET_CONN;
with
GET_CONN;
which sets conn implicitly and asserts that it is non-NULL.
If we actually want to test if conn is non-NULL or behave
differently, then you must use threadlocal_get_conn() instead,
and some existing uses do that.
Rich.