Error: cannot read property right of null

[2000ko]

I am trying to have a group vs group collision however randomly my game sometimes freezes and the error message 'cannot read property right of null' appears. All help would be appreciated,  here is the code I am using to detect the collisions:

 

Group creation:

Monsters = this.add.group();Monsters.enableBody = true;Rockets = this.add.group();Rockets.enableBody = true;

Spawning Rockets:

SpawnRocket: function() {		var rocketN = Rockets.create(player.x + 21.5, player.y, 'Rocket1');		rocketN.name = 'rocketN' + rocketN;		rocketN.body.velocity.y = -600;		this.game.physics.arcade.enable(rocketN);	},

Spawning Monsters:

SpawnMonsters: function() {		this.loop = true;		this.delay = 50;		var RandomN = Monsters.create(this.rnd.integerInRange(0, 850), 0, 'Monster1');		RandomN.name = 'Monster' + RandomN;		RandomN.body.velocity.y = 120;		this.game.physics.arcade.enable(RandomN);				if (score > 10)		{			var RandomN = Monsters.create(this.rnd.integerInRange(0, 850), 0, 'Monster2');			RandomN.name = 'Monster' + RandomN;			RandomN.body.velocity.y = 120;		}},

Collision:

this.physics.arcade.collide(Rockets, Monsters, this.collisionHandler, null, this);

[Skeptron]

Without more code it's hard to help. My guess is that you have empty references in the Rockets or Monsters group.