Facebook Android SDK records "Unknown" App Version for "App Installs" events -

i integrating facebook android sdk can correlate app installs facebook ads running.

i've followed the instructions , i've confirmed events getting logged facebook. i've used jd-gui confirm obfuscation isn't happening on facebook classes.

the weird thing "app installs" events show "app version" of "unknown" (this screenshot shows me filtering "app installs" events):

this might benign (i'm still investigating), know cause? thanks!