Access of possibly undefined property isKeyJump through a reference with static type Function.

public static var isKeyRight:Boolean = false;

public function Cont()
    {
        Cont.isKeyRight = false;
        ... }

if (standing && Cont.isKeyJump) vacc = _jumpAcc;

package {

import flash.display.MovieClip;
import flash.events.Event;

public class PersonnagePrincipal extends Physical {

    //INITIALISATION
    ...

    //CONSTRUCTOR
    public function PersonnagePrincipal(life:Number = 100, focus:Number = 100, lifeMax:Number = 100, focusMax:Number = 100)
    {
        super();
        ...
    }

    // GET & SET
    public function set life(life:Number):void {    _life = (life > lifeMax) ? lifeMax : life;  }
    ...


    // UPDATE
    override public function update(event:Event)
    {
        move_physical();

        if (standing && Cont.isKeyJump) vacc = _jumpAcc;
        ...

package {

import flash.events.Event;
import flash.events.KeyboardEvent;
import flash.ui.Keyboard;
import flash.display.MovieClip;
import flash.utils.*;

public class Cont extends MovieClip
{
    // Key codes
    public static var isKeyRight:Boolean;
    public static var isKeyJump:Boolean;
    ...

    //CONSTRUCTOR
    public function Cont()
    {
        Cont.isKeyRight = false;
        Cont.isKeyJump = false;
        ...

        if (stage) { init(); }
        else { this.addEventListener(Event.ADDED_TO_STAGE, init); }
    }

    //POST-CONSTRUCTOR
    private function init(e:Event=null)
    {
        this.removeEventListener(Event.ADDED_TO_STAGE, init);
        ...
    }