Rule with y=0 does not render

[darthtrevino]

Describe the bug
If a rule mark is made from y={0} to y={100} (and x is some value), it will not render, but if y={0.01}, it will render. And vice versa dimensionally.

Expected behavior
x,y,x2,y2 should all accept 0 as a valid input. If they check for falsiness in determining encoding output, it should be switched to an undefined/null check instead.