No. Without a loss, there can't be a wash sale.

My question was regarding the semantics of the terms “gain” and “loss” according to the IRS, but I just happened to find some answers on page 42 of IRS Publication 550:

“Gain. If the amount you realize from a sale or trade is more than the adjusted basis of the property you transfer, the difference is a gain.

“Loss. If the adjusted basis of the property you transfer is more than the amount you realize, the difference is a loss.”

Hence, “zero” would neither be a loss nor a gain, so I would suppose that wash sales, applying only to losses, could not apply to “zero”. However, if the definitions were the following:

“Gain. If the amount you realize from a sale or trade is not less than the adjusted basis of the property you transfer, the difference is a gain.

“Loss. If the adjusted basis of the property you transfer is not less than the amount you realize, the difference is a loss.”

then “zero” could be both a gain and a loss, meaning that the wash sale rule applying only to losses would include “zero”.

Still, I find that an objective choice between these two pairs of definitions would be somewhat arbitrary, which is why my question had arisen initially.