Fix bug with variable_names=None on reset

pysr/sr.py

@@ -943,7 +943,7 @@ class PySRRegressor(BaseEstimator, RegressorMixin):
 
         assert not isinstance(y, pd.DataFrame)
 
-        if len(variable_names) == 0:
+        if variable_names is None or len(variable_names) == 0:
             variable_names = [f"x{i}" for i in range(X.shape[1])]
 
         use_custom_variable_names = len(variable_names) != 0

pysr/version.py

@@ -1,2 +1,2 @@
 __version__ = "0.7.4"
-__symbolic_regression_jl_version__ = "0.7.8"
+__symbolic_regression_jl_version__ = "0.7.9"