Problems with Line Chart

[Victor Almeida]

Well, i need to create a script that will generate a line chart to demonstrate some data from an any report. 

One of the rules i need to follow is that the chart needs to have the CURVED LINES.

The script contains the command below to do this: 

var chart = sheet.newChart().asLineChart().setOption('curveType', 'function');

But, when the chart is created, the curve goes below 0 (zero), even i don't have negative data.

Example in the image below.

For smaller data, the curve is less noticeable. But still it is something that brings incorrect data as there are no negative records.

I have been looking for solutions to this problem but I have not found anything.

Exist any setting for that? I did something wrong?

Ps: Another thing that bothers me is the vertical axis being negative (-10). But I set the minimum value to zero and the part that is negative hides. But the curve continues to go below zero.

Thanks in advanced.