GetSpeed() not working?

[G3bE]

I tried to print out the users speed with both GetSpeed().x/y/z and GetSpeedX/Y/Z() and it just send me nulls. Is there anything I should know for using this function? Here is my onPlayerMoving() code:

function OnPlayerMoving(Player)
 Player:SendMessageInfo(\'Speed X:\' .. Player:GetSpeed().x)
end

The hook is the same as in "Writing a Cuberite plugin" in the registering hook part.(link postet as a reply)
Sincerely G3bE