fix(condition): fix  where x prime is not parameterized correctly
see
@@ -92,7 +92,7 @@ class IVP(Condition):
`enforce` is meant to be called by the function `solve` and `solve_system`.
"""
x = _network_output(net, t, self.ith_unit)
- if self.x_0_prime:
+ if self.x_0_prime is not None:
return self.x_0 + (t-self.t_0)*self.x_0_prime + ( (1-torch.exp(-t+self.t_0))**2 )*x
else:
return self.x_0 + (1-torch.exp(-t+self.t_0))*x
