What happens to a coinbase transaction when no address is given? The transaction block
This coin base transaction has no valid address for reward. Did we lose that reward bitcoin forever?
In the event that the Coinbase transaction produces outputs that total less than the eligible block reward, any unclaimed coins are permanently lost.
In this specific case, the entire block reward of 12.5 BTC was permanently lost.
There have been other instances where miners only partially claimed the full amount they were able to claim, also leading to a permanent loss.
Note that in scenarios like this, it leads to a reduction of the total supply of bitcoin. There are other types of losses, such as sending coins to an address with no known private key, which don't reduce the total supply.