format(<yearquarter[0]>) fails

[mitchelloharawild]

Underlying issue for https://github.com/tidyverts/feasts/issues/117

format(tsibble::yearquarter())
#> Error in format.POSIXlt(as.POSIXlt(x), ...): invalid 'format' argument

^{Created on 2020-09-17 by the reprex package (v0.3.0)}