My guess is that this is a legit bug, because two other places in that file that use this pattern, also marked with the same for loop comment of ‘// Now we can finish off the emitters.’ handle this condition with the same comment:
if (Handle.GetIsEnabled() && Handle.GetEmitterData()) // Don't pull in the emitter if it isn't going to be used.
FNiagaraEditorModule::PrecompileDuplicate() does not handle this
Thanks for finding this, providing repro steps and reporting.
I took a look at the code and that definitely looks like a bug since the other code does correctly guard against the GetEmitterData(). I’ve filed a public bug ticket for this and attached to this case.