"with_USA" only works by itself, not in conjunction with "linear"

[johanneskoch94]

a <- new.magpie(
  years = 2000,
  cells_and_regions = "AIA",
  names = "foo",
  fill = 1
)

#das gibt NA zurück
GDPuc::convertGDP(
  gdp = a,
  unit_in = "constant 2005 US$MER",
  unit_out = mrdrivers::toolGetUnitDollar(),
  replace_NAs = c("linear", "with_USA")
)

#hätte erwartet, dass dieses ergebnis rauskommt
GDPuc::convertGDP(
  gdp = a,
  unit_in = "constant 2005 US$MER",
  unit_out = mrdrivers::toolGetUnitDollar(),
  replace_NAs = "with_USA"
)

Thanks @fbenke-pik for raising this.