When does placeholder function get called?

Hello,
I implemented getTimeline, getSnapshot and placeholder methods. While getTimeline, getSnapshot methods are getting called as expected, i don't see placeholder ever getting called ( my debug point never hits)

Also, as per my understanding, placeholder is supposed to feed the UI when the data is not available. Since placeholder method never gets called, i see a black widget during transition(when data isn't ready)

Is there a workaround? is anyone else experiencing the same?
When does placeholder function get called?
 
 
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