To Reproduce:

1. Open scene 'OnSecondaryCamera' in the attached project.

2. Chnage script property on the 'Blur' component in the 'Secondary Camera' gameObject to 'Fisheye'.

3. Notice the null/missing reference erros.

4. Try enabling the 'Fisheyey' component from the inspector, notice that this doesn't work and you get nullref exceptions when you click the checkbox.

3. This behavior can be reproduced with other effect as well, i.e. if you change back to blur it behaves the same. Fisheye (and other effects) can be added fine (and it works fine) as a new component.