Scoreboard accepts arguments for @p but if not found it will use a wrong name

if i set up a commandblock with "scoreboard teams join teamname @p[r=4]" it will work.
But if there is no player in a radius of 4 Blocks it will add the player "@p[r=4]" to the team "teamname" instead of doing nothing.
I tried this with many different arguments for @p and @a and it is everytime the same.