PyVISA 1.12.0 and GPIB Secondary Addresses about pyvisa-sim HOT 1 CLOSED

index ccbbe75..a92d324 100644
--- a/pyvisa_sim/gpib.py
+++ b/pyvisa_sim/gpib.py
@@ -24,9 +24,10 @@ class GPIBInstrumentSession(sessions.Session):
         self.attrs[constants.VI_ATTR_GPIB_PRIMARY_ADDR] = int(
             self.parsed.primary_address
         )
-        self.attrs[constants.VI_ATTR_GPIB_SECONDARY_ADDR] = int(
-            self.parsed.secondary_address
-        )
+        if self.parsed.secondary_address is not None:
+            self.attrs[constants.VI_ATTR_GPIB_SECONDARY_ADDR] = int(
+                self.parsed.secondary_address
+            )

     def read(self, count):
         end_char, _ = self.get_attribute(constants.VI_ATTR_TERMCHAR)