message: account for 'conn' being the empty string in some tests
diff: @@ -99,7 +99,7 @@ def read_sql(
  if not protocol:
  # note: redshift/clickhouse are not compatible with the 'binary' protocol, and use other database
  # drivers to connect. set a compatible protocol and masquerade as the appropriate backend.
  - backend, connection_details = conn.split(":",1)
  + backend, connection_details = conn.split(":",1) if conn else ("","")
  if "redshift" in backend:
  conn = f"postgresql:{connection_details}"
  protocol = "cursor"
  