[Bug] Incorrect/missing fill attribute when exproting to SVG

When exporting a shape to SVG that does not have a fill in the design, fill is omitted from the SVG, as in this output:

<rect x="0.5" y="0.5" width="503" height="319" stroke="black"/>

According to the SVG specs, the default value for fill is black. This leads to incorrect output.

When no fill attribute is provided in the design, the fill attribute should be set to “none”. The correct output should be:

<rect x="0.5" y="0.5" width="503" height="319" stroke="black" fill="none" />