help with unhandled exception

var dirviento = cc.windBearing;
var speedviento = cc.windSpeed;
if ((speedviento != null) && (dirviento != null)){
							//dc.drawText(ancho - ancho/4, CY + 10, Gfx.FONT_TINY,speedviento.format("%.1f"),Gfx.TEXT_JUSTIFY_CENTER);
							dc.setPenWidth(Airegrueso(speedviento));
							dc.setColor(AireColor(speedviento),Gfx.COLOR_TRANSPARENT);
							dc.drawLine(WindCtr[0], WindCtr[1], WindPoint[0], WindPoint[1]);
							
							
}
function Airegrueso(aire){
		var grueso;
		if(aire == null || aire < 0.6) {
			grueso = 0;			
		} else if (aire < 1.6 ){
			grueso = 1;
		}else if (aire < 3.1 ){
			grueso = 2;
		}else if (aire < 5.1 ){
			grueso = 3;
		}else if (aire < 8.1 ){
			grueso = 4;
		}else if (aire < 10.6 ){
			grueso = 5;
		}else if (aire < 13.6 ){
			grueso = 6;
		}else if (aire < 16.6 ){
			grueso = 7;
		}else if (aire < 20.1 ){
			grueso = 8;
		}else if (aire < 23.6 ){
			grueso = 9;
		}else if (aire < 27.6 ){
			grueso = 10;
		}else if (aire < 31.6){
			grueso = 11;
		}else {
			grueso = 12;
		}
		return grueso;
	}