Small fix in gammapy/astro/population/spatial.py
@@ -339,7 +339,7 @@ class LogSpiral(object):
elif (radius is None) and not (theta is None):
radius = self.radius(theta, spiralarm_index=spiralarm_index)
else:
- ValueError("Specify only one of: theta, radius")
+ raise ValueError("Specify only one of: theta, radius")
theta = np.radians(theta)
x = radius * cos(theta)
