add missing conditional in gpytorch.kernels.Kernel when active_dims is set
@@ -105,6 +105,8 @@ class Kernel(Module):
x1 = x1_.index_select(-1, self.active_dims)
if x2_ is not None:
x2 = x2_.index_select(-1, self.active_dims)
+ else:
+ x2 = None
else:
x1 = x1_
x2 = x2_
