fixed changes in compare_models

Author: uri.akavia

tests/test_io/conftest.py

@@ -120,8 +120,9 @@ def _compare_models(model_1: Model, model_2: Model) -> None:
         assert model_2.reactions[0]._model is model_2
 
         # gene -> model reference
-        assert model_1.genes[0]._model is model_1
-        assert model_2.genes[0]._model is model_2
+        if model_1.genes:
+            assert model_1.genes[0]._model is model_1
+            assert model_2.genes[0]._model is model_2
 
         # extra comparisons
         # assert model_1.compartments == model_2.compartments