fixed small bug

pybindmagic/__init__.py

@@ -174,6 +174,7 @@ def cpp(line, cell, *what):
             # otherwise we import all names that don't begin with _
             names = [x for x in mdl.__dict__ if not x.startswith("_")]
     except Exception as e:
+        if cmake_path is not None:
             with open(os.path.join(cmake_path,"CMakeLists.txt"), 'w') as f:
                 f.write(cmake)
         if os.path.exists(os.path.join(path,f"{name}.cpp")):