Can't get metadata from underlying fallback source

[danbo]

Can someone help me figure out why I can't access the last_metadata() method of the selected() source of a fallback? Other methods like time() and duration() don't work either but I can get around those by using source.time(actualSource) or source.duration(actualSource)

source script:

silence = blank(id="silence")

me = fallback([silence])

def onTick() = 
  actualSource = me.selected() ?? silence
  meta = actualSource.last_metadata() ?? []
  print(meta)
end

thread.run(every=1., onTick)

output.dummy(me)

INFO: Loading Sdl_image, Target = linux
INFO: Loading Sdl_ttf, Target = linux
At debug/fallback.liq, line 7, char 9-21:
  meta = actualSource.last_metadata() ?? []

Error 5: this value has type
  source('A)
  .{
    buffered? : () -> [string * float],
    duration? : () -> float,
    elapsed? : () -> float,
    fallible? : bool,
    id? : () -> string,
    is_active? : () -> bool,
    is_ready? : () -> bool,
    is_up? : () -> bool,
    last_metadata? : () -> [string * string]?,
    log? : 
    {level : (() -> int?).{set : (int) -> unit}
    },
    on_metadata? : ((([string * string]) -> unit)) -> unit,
    on_shutdown? : ((() -> unit)) -> unit,
    on_track? : ((([string * string]) -> unit)) -> unit,
    on_wake_up? : ((() -> unit)) -> unit,
    remaining? : () -> float,
    seek? : (float) -> float,
    self_sync? : () -> bool,
    skip? : () -> unit,
    time? : () -> float
  } where 'A is a set of internal tracks (inferred at debug/fallback.liq, line 6, char 17-41)
but it should be a subtype of the type of the value at debug/fallback.liq, line 7, char 9-37
  'A.{last_metadata : 'B}

on

Liquidsoap 2.2.2
Copyright (c) 2003-2023 Savonet team
Liquidsoap is open-source software, released under GNU General Public License.
See <http://liquidsoap.info> for more information.

and

Liquidsoap 2.2.3+git@fece51da6
Copyright (c) 2003-2023 Savonet team
Liquidsoap is open-source software, released under GNU General Public License.
See <http://liquidsoap.info> for more information.