BUG? "unresolved variable" in Webstorm IDE ES6

[Kimely]

https://github.com/Kimel1/Test/  

index.js:25

this.balls.body.velocity.setTo(0, 0);

velocity = "unresolved variable" 

but  when I compile project I have no errors and this function works normal. 
For other function Webstorm don't display any errors. 

I think that problem is that

game.physics.arcade.enable(this.balls);

change type of body in Phaser.Sprite (phaser)  and it is very complex for IDE.

Can I set physics 

this.balls.body.velocity.setTo(0, 0);

in more simple way that IDE can understand it?