Sampler1DRfun gives wrong result for $sample(0)

[mb706]

$sample(0) should return an empty design, but Sampler1DRfun returns a design with one NA-valued row:

Sampler1DRfun$new(param = ParamDbl$new("x", 0, 10), rfun = function(n) numeric(0))$sample(0)
#> <Design> with 1 rows:
#>     x
#> 1: NA

Expected is what other samplers do:

Sampler1DUnif$new(param = ParamDbl$new("x", 0, 10))$sample(0)
#> <Design> with 0 rows:
#> Empty data.table (0 rows and 1 cols): x