The standard response is "no, the reward is at least one transaction." What about after there is no more reward?
Outputs with 0 value are valid (but non-standard). When the block subsidy reaches 0, blocks without fees will need to produce coinbase transactions with 0-value outputs. Every block must have a coinbase transaction.
That is far in the future and can still be changed, but at the current time a coinbase transaction is required and will always be present. It is very likely that this rule will be upheld in the future as well. It is also possible that the transaction accuracy could be increased enough for there to always be a block reward, however minuscule.