Using Collision in Niagara without an Update Age module will prevent any particles from spawning

Using Collision without Update Age will prevent any particles from spawning. In Collision Query and Response DataInstance.Alive has a default value of false. If no other module sets DataInstance.Alive to true, this default value will be used, and cause all particles to be killed immediately.

WORKAROUND:
Set DataInstance.Alive to true directly in the stack.

1. Create a new Niagara System based off the the Fountain template
2. Add a Collision module to the Particle Update
3. Disable the Update Age module

RESULT:
The emitter no longer has any particles. Re-enabling Update Age will start spawning particles again.