I understand how the bubble graph works, and it's working fine with elements with x / y values greater than 0. I also fixed this adding 0.01 to each value, because it's close enough and not equal to 0.
If you tell me x=0 and y=0 are not valid values, I can understand it, but it may need a revision, as in my graph currently x=0 and y=0 values are valid values and must be rendered.
Anyway, i think it's a division by zero bug, gettin max-x (which is 0) and calculating the division lines by dividing something by max-x.