The output used is a native segwit output. If you look at the transaction that created it, you get
0014644a61cf83439e53b5dd413bec63c98c9e39c107 for the lock script, which is a native p2wpkh segwit output.
Spend a purely segwit output does not require any value for the scriptSig (unlike a p2sh-p2wpkh).
The address is displayed as unanalyzed because Insight has not been updated to recognize bech32 addresses.