How do I not compare a "number with a nil?"

function assignScientists(amount)
   local valid_players = {}
   local player = game.Players:GetChildren()
   if(#player>0)then
   for p = 1, #player do
   if(player[p].TeamColor==Americans_team.TeamColor)and
   (player[p].Character~=nil)then
   table.insert(valid_players,player[p])
   end
   end
   end
   if(#valid_players>amount)then
   while(amount>0)do
   local rand = math.random(1,#valid_players)
   local chosen = valid_players[rand]
   chosen.TeamColor = Europeans_team.TeamColor
   chosen.Character.Humanoid.Health = 0

   table.remove(valid_players,rand)
   amount = amount -1
   end
   end
 end
 assignScientists()

In the output value, it kept saying "attempt to compare number with a nil" at line 13. I put a 0 there but yet it still says the same thing. Can anyone help me? Thank you for reading.

function assignScientists(amount) -- This function is looking for a parameter
   local valid_players = {}
   local player = game.Players:GetChildren()
   if(#player>0)then
   for p = 1, #player do
   if(player[p].TeamColor==Americans_team.TeamColor)and
   (player[p].Character~=nil)then
   table.insert(valid_players,player[p])
   end
   end
   end
   if(#valid_players>amount)then
   while(amount>0)do
   local rand = math.random(1,#valid_players)
   local chosen = valid_players[rand]
   chosen.TeamColor = Europeans_team.TeamColor
   chosen.Character.Humanoid.Health = 0

   table.remove(valid_players,rand)
   amount = amount -1
   end
   end
 end
 assignScientists() --You have no parameters

Try adding a parameter to assignScientists() at the bottom. This may fix the issue with amount being nil.

Example: assignScientists(0)

 function playScientists()
     if countPlayers()<=3 then
     assignScientists(1)

Well, I added another code that was like this but it didn't work.